Method for forming pattern using a photomask

ABSTRACT

A photomask has a semi-light-shielding portion having a light-shielding property and a light-transmitting portion surrounded by the semi-light-shielding portion, and a peripheral portion positioned in the periphery of the light-transmitting portion. The semi-light-shielding portion and the light-transmitting portion transmit exposure light in the same phase, whereas the peripheral portion transmits exposure light in a phase opposite to that of the light-transmitting portion.

BACKGROUND OF THE INVENTION

The present invention relates to a photomask for forming a fine patternused for producing a semiconductor integrated circuit device, a methodfor producing the same and a method for forming a pattern using thephotomask.

In recent years, it is increasingly necessary to miniaturize circuitpatterns for high integration of a large-scale integrated circuit device(hereinafter, referred to as “LSI”) that can be realized withsemiconductors. As a result, a reduction of the width of a line forwiring patterns constituting a circuit or miniaturization of contacthole patterns (hereinafter, referred to as “contact patterns”) thatconnect between layered wirings formed via insulating layers have becomevery important.

Hereinafter, miniaturization of wiring patterns with a recentlight-exposure system will be described by taking the case of using apositive resist process as an example. In a positive resist process, aline pattern refers to a line-shaped resist film (resist pattern) thatare left, corresponding to a non-exposed region of a resist by exposurewith a photomask and subsequent development. A space pattern refers to aportion from which a resist is removed (resist-removed pattern)corresponding to an exposed region of a resist. A contact pattern refersto a hole-like resist-removed portion and can be regarded as a smallspace pattern of the space patterns. When using a negative resistprocess instead of a positive resist process, the definition of the linepattern and the definition of the space pattern are replaced by eachother.

In general, for miniaturization of wiring patterns, a method for forminga fine line pattern with oblique incident light exposure (off-axisillumination) called super resolution exposure has been used. Thismethod is an excellent method for miniaturization of a resist patterncorresponding to a non-exposed region of a resist, and also has aneffect of improving the depth of focus of dense patterns that arearranged periodically. However, this oblique incident exposure methodhas little effect on miniaturization of isolated resist-removedportions, and on the contrary, this method deteriorates the contrast ofimages (optical images) and the depth of focus. Therefore, the obliqueincident exposure method is positively used to form patternscharacterized in that the size of the resist-removed portion is largerthan the size of a resist pattern, for example, to form gate patterns.

On the other hand, to form a micro resist-removed portion that isisolated such as a small contact pattern, it is known that it is usefulto use a small light source having a low coherence degree that containsno oblique incident component. In this case, it is more useful to use ahalf-tone phase-shifting mask (see, for example, Japanese Laid-OpenPatent Publication No. 9-90601). In the half-tone phase-shifting mask, aphase sifter that has a very low transmittance of about 3 to 6% withrespect to exposure light and that causes phase inversion of 180 degreeswith respect to light transmitted through an opening, instead of acomplete light-shielding portion, is provided as a mask patternsurrounding a light-transmitting portion (opening) corresponding to acontact pattern.

In this specification, a transmittance is represented by an effectivetransmittance when the transmittance of a transparent substrate is takenas 100%, unless otherwise specified. Moreover, “complete light-shieldingfilm (complete -light-shielding portion) refers to a light-shieldingfilm (light-shielding portion) having an effective transmittance ofsmaller than 1 %.

Hereinafter, the principle of the method for forming patterns using ahalf-tone phase-shifting mask will be described with reference to FIGS.27A to 27G.

FIG. 27A is a plan view of a photomask in which an opening correspondingto a contact pattern is provided in a chromium film serving as acomplete light-shielding portion provided on the surface of the mask.FIG. 27B shows the amplitude intensity corresponding to line AA′ oflight transmitted through the photomask shown in FIG. 27A. FIG. 27C is aplan view of a photomask in which a chromium film corresponding to acontact pattern as a complete light-shielding portion is provided in aphase shifter provided on the surface of the mask. FIG. 27D shows theamplitude intensity corresponding to line AA′ of light transmittedthrough the photomask shown in FIG. 27C. FIG. 27E is a plan view of aphotomask in which an opening corresponding to a contact pattern isprovided in a phase shifter provided on the surface of the mask (i.e., ahalf-tone phase-shifting mask). FIGS. 27F and 28G show the amplitudeintensity and the light intensity corresponding to line AA′ of lighttransmitted through the photomask shown in FIG. 27E, respectively.

As shown in FIGS. 27B, 27D, and 27F, the amplitude intensity of lighttransmitted through the half-tone phase-shifting mask shown in FIG. 27Eis equal to the sum of the amplitude intensities of lights transmittedthrough the photomasks shown in FIGS. 27A and 27C. That is to say, inthe half-tone phase-shifting mask shown in FIG. 27E, the phase shifterserving as a light-shielding portion is configured so as to not onlytransmit light at a low transmittance, but also provide an optical pathdifference (phase difference) of 180 degrees with respect to the lighttransmitted through the opening to the light transmitted through thisphase shifter. Therefore, as shown in FIGS. 27B and 27D, the lighttransmitted through the phase shifter has an amplitude intensity with aphase opposite to that of the light transmitted through the opening.Thus, if the amplitude intensity distribution shown in FIG. 27B and theamplitude intensity distribution shown in FIG. 27D are synthesized, aphase boundary in which the amplitude intensity is turned to 0 by aphase change is generated, as shown in FIG. 27F. As a result, as shownin FIG. 27G, in the end of the opening that is the phase boundary(hereinafter, referred to as a “phase end”), the light intensity, whichis represented by a square of the amplitude intensity, becomes 0, and asignificantly dark portion is formed. Accordingly, in an image of thelight transmitted through the half-tone phase-shifting mask shown inFIG. 27E, strong contrast is realized in the vicinity of the opening.However, the following should be noted: This improvement of the contrastoccurs with respect to light vertically incident to the mask, morespecifically, that is, light incident to the mask from a small lightsource region having a low coherence degree. However, the contrast isnot improved even in the vicinity of the opening (in the vicinity of thephase boundary in which a phase change occurs) with respect to obliqueincident exposure light, for example, exposure called annularillumination in which a vertical incident component (illuminationcomponent from the center of a light source (the normal direction of themask) is removed. Furthermore, there is another disadvantage in thatcompared with the case where exposure is performed with a small lightsource having a low coherence degree, the depth of focus is lower in thecase where oblique incident exposure is performed.

As described above, in order to form a fine resist-removed pattern suchas a contact pattern using a positive resist process, it was necessaryto perform exposure with a small light source having a coherence degreeof about 0.5 or less, which provides illumination only with verticalincident components, in combination with a half-tone phase-shiftingmask. This method was very useful to form fine and isolated contactpatterns.

There is a recent tendency associated with a high degree of integrationof recent semiconductor devices that densely arranged patterns as wellas isolated patterns are also required not only for wiring patterns butalso contact patterns. In order to realize a high depth of focus whenforming densely arranged contact patterns, oblique incident exposure isuseful as in the case of the densely arranged wiring patterns.

Furthermore, in recent years, also when forming wiring patterns, inaddition to miniaturization of line patterns serving as wiring patterns,there is an increasing demand for miniaturization of space patternsbetween wirings. As in the case of the isolated contact patterns, it isuseful to use a light source having a low coherence degree incombination with a half-tone phase-shifting mask in order to form smallisolated space patterns between wirings.

That is to say, although oblique incident exposure is essential to formhigh density wiring patterns and high density contact patterns, thecontrast and the depth of focus of isolated contact patterns andisolated space patterns between wirings are significantly deterioratedwhen oblique incident exposure is performed. The contrast and the depthof focus are deteriorated even more significantly when a half-tonephase-shifting mask is used to improve the resolution.

On the other hand, when a small light source having a low coherencedegree is used to form small isolated contact patterns and smallisolated space patterns between wirings, it becomes difficult to formhigh density patterns or small line patterns.

Therefore, the optimal illumination conditions with respect to smallisolated space patterns and the optical illumination conditions withrespect to densely arranged patterns or small line patterns have acontradictory relationship. Therefore, in order to form small resistpatterns and small isolated resist-removed patterns at the same time, alight source having a medium coherence degree (about 0.5 to 0.6) is usedfor a trade-off between the effect of vertical incident components froma light source and the effect of oblique incident components from alight source. However, in this case, both the effect of verticalincident components and the effect of oblique incident components arecanceled, so that it is difficult to realize further high integration ofsemiconductor devices by miniaturizing isolated line patterns or denselyarranged patterns and isolated space patterns at the same time.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to miniaturize isolated space patterns and isolated linepatterns or dense patterns at the same time.

In order to achieve the above object, a first photomask of the presentinvention includes on a transparent substrate: a semi-light-shieldingportion having a light-shielding property with respect to exposurelight: a light-transmitting portion surrounded by thesemi-light-shielding portion and having a light-transmitting propertywith respect to exposure light: and a peripheral portion surrounded bythe semi-light-shielding portion and positioned in a periphery of thelight-transmitting portion. The semi-light-shielding portion and thelight-transmitting portion transmit the exposure light in the samephase. The peripheral portion transmits the exposure light in a phaseopposite to that of the semi-light-shielding portion and thelight-transmitting portion. The surface of the transparent substrate ina formation region for the light-transmitting portion is exposed. Afirst phase shift film that transmits the exposure light in a phaseopposite to that of the light-transmitting portion is formed on thetransparent substrate in a formation region for the peripheral portion.The first phase shift film and a second phase shift film that transmitsthe exposure light in a phase opposite to that of the light-transmittingportion are laminated sequentially on the transparent substrate in aformation region for the semi-light-shielding portion. A multilayeredstructure of the first phase shift film and the second phase shift filmhas a transmittance that allows the exposure light to be transmittedpartially and transmits the exposure light in the same phase as that ofthe light-transmitting portion.

According to the first photomask, a peripheral portion that transmitsexposure light in a phase opposite to that of a light-transmittingportion is sandwiched by the light-transmitting portion and asemi-light-shielding portion having a light-shielding property thattransmits the exposure light in the same phase as that of thelight-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated-resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure(off-axis illumination), for example, in the positive resist process.That is to say, it is possible to miniaturize isolated space patternsand isolated line patterns or dense patterns at the same time bycombining the first photomask and oblique incident exposure.

Furthermore, according to the first photomask, the transmittance of theperipheral portion can be defined by the single layered structure of thefirst phase shift film, and the transmittance of thesemi-light-shielding portion can be defined by the multilayeredstructure of the first phase shift film and the second phase shift film,so that a combination of the transmittance of the peripheral portion andthe semi-light-shielding portion can be set arbitrarily.

In this specification, “having light-transmitting properties withrespect to exposure” means having a transmittance that allows a resistto be exposed, and “having light-shielding properties with respect toexposure” means having a transmittance that does not allow a resist tobe exposed. The “same phase” means a phase difference y of (−30+360×n)degrees or more and (30+360×n) degrees or less, (where n=an integer),and the “opposite phase” means a phase difference of (150+360×n) degreesor more and (210+360×n) degrees or less.

In the first photomask, it is preferable that the first phase shift filmhas a first transmittance adjusting film and a first phase adjustingfilm formed on the first transmittance adjusting film, the firsttransmittance adjusting film transmits the exposure light in the samephase as that of the light-transmitting portion and has a relatively lowtransmittance with respect to the exposure light, and the first phaseadjusting film transmits the exposure light in a phase opposite to thatof the light-transmitting portion and has a relatively hightransmittance with respect to the exposure light.

With this embodiment, a combination of a desired phase difference and adesired transmittance can be selected arbitrarily for the first phaseshift film, and a combination of the material of the transmittanceadjusting film and the material of the phase adjusting film makes itpossible to improve the selection ratio at etching for processing thefirst phase shift film.

In the first photomask, it is preferable that the second phase shiftfilm has a second transmittance adjusting film and a second phaseadjusting film formed on the second transmittance adjusting film, thesecond transmittance adjusting film transmits the exposure light in thesame phase as that of the light-transmitting portion and has arelatively low transmittance with respect to the exposure light, and thesecond phase adjusting film transmits the exposure light in a phaseopposite to that of the light-transmitting portion and has a relativelyhigh transmittance with respect to the exposure light.

With this embodiment, a combination of a desired phase difference and adesired S transmittance can be selected arbitrarily for the second phaseshift film, and a combination of the material of the transmittanceadjusting film and the material of the phase adjusting film makes itpossible to improve the selection ratio at etching for processing thesecond phase shift film.

In the first photomask, the peripheral portion may be in contact withthe light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

In the first photomask, it is preferable that the first phase shift filmhas a first phase adjusting film that transmits the exposure light in aphase opposite to that of the light-transmitting portion, the secondphase shift film has a second phase adjusting film that is formed on thefirst phase adjusting film and transmits the exposure light in a phaseopposite to that of the light-transmitting portion, and a transmittanceadjusting film having a lower transmittance than that of the phaseadjusting films with respect to the exposure light is formed between thefirst phase adjusting film and the second phase adjusting film.

With this embodiment, the semi-light-shielding portion has a structurein which a transmittance adjusting film having a low transmittance isprovided between the first phase adjusting film and the second phaseadjusting film, and therefore the difference in transmittance betweenthe semi-light-shielding portion and the peripheral portion can beincreased, so that the contrast in the light intensity distributionbetween the light-transmitting portion and the peripheral portion can beenhanced more. Furthermore, when the structure in which thetransmittance adjusting film is formed partially on the first phaseadjusting film in the peripheral portion formation region is used, theeffective transmittance of the peripheral portion can be adjusted finelyby the area ratio of the peripheral portion that is covered with thetransmittance adjusting film (=(the area of the transmittance adjustingfilm in the peripheral portion formation region)/(the area of theperipheral portion)). Therefore, it is possible to arbitrarily changethe transmittance of the peripheral portion depending on the patternshape on the same photomask.

In the photomask, it is preferable that the transmittance of thesemi-light-shielding portion with respect to the exposure light is 6% ormore and 15% or less.

With this embodiment, the contrast enhancement effect by the firstphotomask can be obtained reliably while preventing a reduction inthickness of the resist film in pattern formation.

A second photomask of the present invention includes on a transparentsubstrate: a semi-light-shielding portion having a light-shieldingproperty with respect to exposure light: a light-transmitting portionsurrounded by the semi-light-shielding portion and having alight-transmitting property with respect to exposure light: and aperipheral portion surrounded by the semi-light-shielding portion andpositioned in a periphery of the light-transmitting portion. Thesemi-light-shielding portion and the light-transmitting portion transmitthe exposure light in the same phase. The peripheral portion transmitsthe exposure light in a phase opposite to that of thesemi-light-shielding portion and the light-transmitting portion. Thesurface of the transparent substrate in a formation region for thelight-transmitting portion is exposed. A semi-light-shielding film thathas a transmittance allowing the exposure light to be transmittedpartially and transmits the exposure light in the same phase to that ofthe light-transmitting portion is formed on the transparent substrate inthe semi-light-shielding portion formation region. Thesemi-light-shielding film with a reduced thickness is formed on thetransparent substrate in a formation region for the peripheral portion,the thickness being such an extent that the exposure light istransmitted in a phase opposite to that of the light-transmittingportion.

According to the second photomask, a peripheral portion that transmitsexposure light in a phase opposite to that of a light-transmittingportion is sandwiched by the light-transmitting portion and asemi-light-shielding portion having a light-shielding property thattransmits the exposure light in the same phase as that of thelight-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure,for example, in the positive resist process. That is to say, it ispossible to miniaturize isolated space patterns and isolated linepatterns or dense patterns at the same time by combining the secondphotomask and oblique incident exposure.

Furthermore, according to the second photomask, the semi-light-shieldingportion is constituted by a single layered structure of thesemi-light-shielding film, so that the mask structure is very simple.Moreover, a peripheral portion can be formed easily simply by partiallyreducing the thickness of the semi-light-shielding film, in other words,by providing a recess in the light-shielding film. Furthermore, also inthe case where a semi-light-shielding portion having a small width ispresent between the peripheral portion and the light-transmittingportion, peeling of the film constituting the semi-light-shieldingportion having a small width can be suppressed, compared with the casewhere a semi-light-shielding portion of a multilayered film structure isused.

In the second photomask, it is preferable that the semi-light-shieldingfilm has a transmittance adjusting film formed on the transparentsubstrate and a phase adjusting film formed on the transmittanceadjusting film. The transmittance adjusting film transmits the exposurelight in the same phase as that of the light-transmitting portion andhas a relatively low transmittance with respect to the exposure light,and the phase adjusting film has a relatively high transmittance withrespect to the exposure light. The phase adjusting film in a formationregion for the semi-light-shielding portion has a thickness thattransmits the exposure light in the same phase as that of thelight-transmitting portion. The phase adjusting film in a formationregion for the peripheral portion has a thickness that transmits theexposure light in a phase opposite to that of the light-transmittingportion.

With this embodiment, a combination of a desired phase difference and adesired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

In the second photomask, it is preferable that the semi-light-shieldingfilm has a phase adjusting film formed on the transparent substrate anda transmittance adjusting film formed only on the phase adjusting filmin the semi-light-shielding portion formation region, the transmittanceadjusting film transmits the exposure light in the same phase as that ofthe light-transmitting portion and has a relatively low transmittancewith respect to the exposure light, the phase adjusting film has arelatively high transmittance with respect to the exposure light, thephase adjusting film in a formation region for the semi-light-shieldingportion has a thickness that transmits the exposure light in the samephase as that of the light-transmitting portion, and the phase adjustingfilm in a formation region for the peripheral portion has a thicknessthat transmits the exposure light in a phase opposite to that of thelight-transmitting portion.

With this embodiment, a combination of a desired phase difference and adesired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

In the second photomask the peripheral portion may be in contact withthe light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

In the second photomask, it is preferable that the transmittance of thesemi-light-shielding portion with respect to the exposure light is 6% ormore and 15% or less.

With this embodiment, the contrast enhancement effect by the secondphotomask can be obtained reliably while preventing a reduction inthickness of the resist film in pattern formation.

A third photomask of the present invention include on a transparentsubstrate: a semi-light-shielding portion having a light-shieldingproperty with respect to exposure light: a light-transmitting portionsurrounded by the semi-light-shielding portion and having alight-transmitting property with respect to exposure light: and aperipheral portion surrounded by the semi-light-shielding portion andpositioned in a periphery of the light-transmitting portion. Thesemi-light-shielding portion and the light-transmitting portion transmitthe exposure light in the same phase. The peripheral portion transmitsthe exposure light in a phase opposite to that of thesemi-light-shielding portion and the light-transmitting portion. Thesurface of the transparent substrate in a formation region for thelight-transmitting portion is exposed. A semi-light-shielding film thathas a transmittance that allows the exposure light to be transmittedpartially and transmits the exposure light in the same phase as that ofthe light-transmitting portion is formed on the transparent substrate inthe semi-light-shielding portion. The transparent substrate in aformation region for the peripheral portion is dug down so as to have athickness that transmits the exposure light in a phase opposite to thatof the light-transmitting portion.

According to the third photomask, a peripheral portion that transmitsexposure light in a phase opposite to that of a light-transmittingportion is sandwiched by the light-transmitting portion and asemi-light-shielding portion having a light-shielding property thattransmits the exposure light in the same phase as that of thelight-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure,for example, in the positive resist process. That is to say, it ispossible to miniaturize isolated space patterns and isolated linepatterns or dense patterns at the same time by combining the thirdphotomask and oblique incident exposure.

Furthermore, according to the third photomask, the semi-light-shieldingportion is constituted by a single layered structure of thesemi-light-shielding film, so that the mask structure is very simple.

In the third photomask, it is preferable that the semi-light-shieldingfilm has a transmittance adjusting film formed on the transparentsubstrate and a phase adjusting film formed on the transmittanceadjusting film, the transmittance adjusting film has a relatively lowtransmittance with respect to the exposure light, and the phaseadjusting film has a relatively high transmittance with respect to theexposure light.

With this embodiment, a combination of a desired phase difference and adesired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

In the third photomask, the peripheral portion may be in contact withthe light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

In the third photomask, it is preferable that the transmittance of thesemi-light-shielding portion with respect to the exposure light is 6% ormore and 15% or less.

With this embodiment, the contrast enhancement effect by the thirdphotomask can be obtained reliably while preventing a reduction inthickness of the resist film in pattern formation.

A method for forming a pattern of the present invention, which useseither one of the first to the third photomasks, includes the steps of:forming a resist film on a substrate; irradiating the resist film withthe exposure light via the photomask, and developing the resist filmirradiated with the exposure light so as to pattern the resist film.

According to the method for forming a pattern of the present invention,the same effects as those of the first to the third photomasks of thepresent invention can be obtained. The above effects can be obtainedreliably by using off-axis illumination (oblique incident exposure) inthe step of irradiating the resist film with the exposure light.

A first method for producing a photomask of the present invention is amethod for producing the photomask including a semi-light-shieldingportion having a light-shielding property with respect to exposurelight: a light-transmitting portion surrounded by thesemi-light-shielding portion and having a light-transmitting propertywith respect to exposure light: and a peripheral portion surrounded bythe semi-light-shielding portion and positioned in a periphery of thelight-transmitting portion on a transparent substrate. Morespecifically, the method includes a first step of forming a first phaseshift film that transmits the exposure light in a phase opposite to thatof the light-transmitting portion on the transparent substrate, and asecond step of forming a second phase shift film that transmits theexposure light in a phase opposite to that of the light-transmittingportion on the first phase shift film, a third step of removing thesecond phase shift film in a formation region for the light-transmittingportion and a formation region for the peripheral portion, and a fourthstep of removing the first phase shift film in the light-transmittingportion formation region after the third step. A multilayered structureof the first phase shift film and the second phase shift film formed onthe transparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in the same phaseas that of the light-transmitting portion.

According to the first method for producing a photomask, the first andthe second phase shift films that transmit exposure light with a phaseinversion are formed sequentially on the transparent substrate. Then,the second phase shift film in the light-transmitting portion formationregion and the peripheral portion formation region is removed.Thereafter, the first phase shift film in the light-transmitting portionformation region is removed. That is to say, the light-transmittingportion is made of the exposed portion of the transparent substrate, andthe semi-light-shielding portion is made of a multilayered structure ofthe first phase shift film and the second phase shift film. Theperipheral portion is made of a single layered structure of the firstphase shift film. The multilayered structure of the first and the secondphase shift films transmits exposure light in the same phase as that ofthe light-transmitting portion. Therefore, the peripheral portion thattransmits exposure light in the phase opposite to that of thelight-transmitting portion is sandwiched by the light-transmittingportion and the semi-light-shielding portion that transmits exposurelight in the same phase as that of the light-transmitting portion. As aresult, the contrast in the light intensity distribution between thelight-transmitting portion and the peripheral portion can be enhanced bymutual interference between the light transmitted through thelight-transmitting portion and the light transmitted through theperipheral portion. This contrast enhancement effect also can beobtained when a fine isolated resist-removed portion (i.e., a fmeisolated space pattern corresponding to the light-transmitting portion)is formed with oblique incident exposure, for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

According to the first method for producing a photomask, the first andthe second phase shift films that are laminated on the transparentsubstrate are etched selectively, so that a mask pattern with any shapethat has the semi-light-shielding portion and the peripheral, portioncan be easily realized.

Furthermore, according to the first method for producing a photomask,when the light-transmitting portion and the peripheral portion areapart, in other words, when a semi-light-shielding portion made of themultilayered structure of the first and the second phase shift films ispresent between the light-transmitting portion and the peripheralportion, the first phase shift film can be etched in a self-alignmentmanner, using the patterned second phase adjusting film as a mask.Therefore, photomask process can be performed precisely.

A second method for producing a photomask of the present invention is amethod for producing the photomask including a semi-light-shieldingportion having a light-shielding property with respect to exposurelight: a light-transmitting portion surrounded by thesemi-light-shielding portion and having a light-transmitting propertywith respect to exposure light: and a peripheral portion surrounded bythe semi-light-shielding portion and positioned in a periphery of thelight-transmitting portion on a transparent substrate. Morespecifically, the method includes a first step of forming a first phaseshift film that transmits the exposure light in a phase opposite to thatof the light-transmitting portion on the transparent substrate, and asecond step of forming a second phase shift film that transmits theexposure light in a phase opposite to that of the light-transmittingportion on the first phase shift film, a third step of removing thesecond phase shift film in a formation region for the peripheralportion, and a fourth step of removing the second phase shift film andthe first phase shift film in the light-transmitting portion formationregion sequentially after the third step. In a multilayered structure ofthe first phase shift film and the second phase shift film formed on thetransparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in the same phaseas that of the light-transmitting portion.

According to the second method for producing a photomask, the first andthe second phase shift films that transmit exposure light with a phaseinversion are formed sequentially on the transparent substrate. Then,the second phase shift film in the peripheral portion formation regionis removed. Thereafter, the second phase shift film and the first phaseshift film in the light-transmitting portion formation region areremoved That is to say, the light-transmitting portion is made of theexposed portion of the transparent substrate, and thesemi-light-shielding portion is made of a multilayered structure of thefirst phase shift film and the second phase shift film. The peripheralportion is made of a single layered structure of the first phase shiftfilm. The multilayered structure of the first and the second phase shiftfilms transmits exposure light in the same phase as that of thelight-transmitting portion. Therefore, the peripheral portion thattransmits exposure light in the phase opposite to that of thelight-transmitting portion is sandwiched by the light-transmittingportion and the semi-light-shielding portion that transmits exposurelight in the same phase as that of the light-transmitting portion.Therefore, the contrast in the light intensity distribution between thelight-transmitting portion and the peripheral portion can be enhanced bymutual interference between the light transmitted through thelight-transmitting portion and the light transmitted through theperipheral portion. This contrast enhancement effect also can beobtained when a fine isolated resist-removed portion (i.e., a fineisolated space pattern corresponding to the light-transmitting portion)is formed with oblique incident exposure, for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

According to the second method for producing a photomask, the first andthe second phase shift films that are laminated on the transparentsubstrate are etched selectively, so that a mask pattern with any shapethat has the semi-light-shielding portion and the peripheral portion canbe easily realized.

Furthermore, according to the second method for producing a-photomask,the step of removing the second phase shift film in the peripheralportion formation region and the step of removing the second phase shiftfilm in the light-transmitting portion formation region are performedseparately. Therefore, when the light-transmitting portion and theperipheral portion are apart by a small distance, in other words, whenthe semi-light-shielding portion having a small width made of themultilayered structure of the first and the second phase shift films ispresent between the light-transmitting portion and the peripheralportion, the margin for photomask processing is increased.

In the first and the second methods for producing a photomask, it ispreferable that the transmittance of the semi-light-shielding portionwith respect to the exposure light is 6% or more and 15% or less.

With this embodiment, the contrast enhancement effect by the first andthe second methods for producing a photomask can be obtained reliablywhile preventing a reduction in thickness of the resist film in patternformation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G are diagrams illustrating the principle of the outlineenhancement method of the present invention.

FIGS. 2A to 2F are diagrams illustrating the dependence of theconventional image enhancement effect utilizing a phase end on the shapeof a light source.

FIGS. 3A to 3F are diagrams illustrating the limit of the size of aphase shifter in the outline enhancement method of the presentinvention.

FIGS. 4A and 4B are diagrams illustrating the limit of the size of aphase shifter in the outline enhancement method of the presentinvention.

FIGS. 5A to 5F are diagrams illustrating the light intensitydistribution produced by exposure light incident from various lightsource positions in forming isolated patterns with an outlineenhancement mask of the present invention.

FIGS. 6A to 6F are diagrams illustrating the light intensitydistribution produced by exposure light incident from various lightsource positions in forming isolated patterns with a conventionalhalf-tone phase-shifting mask.

FIGS. 7A to 7F are diagrams illustrating the dependence of the contrastand the DOF on the transmittance of a semi-light shielding portion inthe outline enhancement mask of the present invention.

FIGS. 8A to 8F are diagrams illustrating variations of the layout of alight shielding mask patterns constituted by a semi-light shieldingportion and a phase shifter in the outline enhancement mask providedwith an opening corresponding to a contact pattern.

FIG. 9A shows a view showing an example of a desired pattern to beformed with a photomask of a first embodiment of the present invention.FIG. 9B is a plan view of the photomask of the first embodiment of thepresent invention. FIG. 9C is a cross-sectional view taken along lineAA′ in FIG. 9B.

FIG. 10A is a cross-sectional view of the photomask of the firstembodiment of the present invention in which each of a lower phaseshifter and an upper phase shifter is a single layered film. FIG. 10B isa cross-sectional view of the photomask of the first embodiment of thepresent invention in which each of a lower phase shifter and an upperphase shifter is a multilayered film of a transmittance adjusting filmand a phase adjusting film.

FIG. 11A is a view showing the shape of a regular exposure light source.FIG. 11B is a view showing the shape of an annular exposure lightsource. FIG. 11C is a view showing the shape of a quadrupole exposurelight source. FIG. 11D is a view showing the shape of anannular—quadrupole mixed type exposure light source.

FIGS. 12A to 12D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the first embodiment ofthe present invention.

FIGS. 13A to 13E are cross-sectional views showing the processes of amethod producing the photomask of the first embodiment of the presentinvention. FIG. 13F is a plan view corresponding to the cross-sectionalview of FIG. 13C, and FIG. 13G is a plan view corresponding to thecross-sectional view of FIG. 13E.

FIGS. 14A to 14E are cross-sectional views showing the processes of amethod producing the photomask of a first variation of the firstembodiment of the present invention. FIG. 14F is a plan viewcorresponding to the cross-sectional view of FIG. 14C, and FIG. 14G is aplan view corresponding to the cross-sectional view of FIG. 14E.

FIGS. 15A to 15E are cross-sectional views showing the processes of amethod producing the photomask of a second variation of the firstembodiment of the present invention. FIG. 15F is a plan viewcorresponding to the cross-sectional view of FIG. 15C, and FIG. 15G is aplan view corresponding to the cross-sectional view of FIG. 15E.

FIG. 16A is a view showing an example of a desired pattern to be formedwith the photomask of a second embodiment of the present invention. FIG.16B is a plan view of the photomask of the second embodiment of thepresent invention. FIG. 16C is a cross-sectional view taken along lineAA′ of FIG. 16B.

FIGS. 17A to 17D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the second embodiment ofthe present invention.

FIGS. 18A to 18D are views showing variations of the cross-sectionalstructure of the photomask of the second embodiment of the presentinvention.

FIG. 19A is a view showing an example of a desired pattern to be formedwith the photomask of a third embodiment of the present invention. FIG.19B is a plan view of the photomask of the third embodiment of thepresent invention. FIG. 19C is a cross-sectional view taken along lineAA′ of FIG. 19B.

FIGS. 20A to 20D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the third embodiment ofthe present invention.

FIGS. 21A and 21B are a plan view and a cross-sectional view of thephotomask of the third embodiment of the present invention in which athin portion of a half-tone film is in contact with an opening,respectively. FIGS. 21C and 211D are a plan view and a cross-sectionalview of the photomask of the third embodiment of the present inventionin which a thin portion of a half-tone film is apart from an opening bya predetermined distance, respectively.

FIG. 22A is a view showing an example of a desired pattern to be formedwith the photomask of a fourth embodiment of the present invention. FIG.22B is a plan view of the photomask of the fourth embodiment of thepresent invention. FIG. 22C is a cross-sectional view taken along lineAA′ of FIG. 22B.

FIGS. 23A to 23D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the fourth embodiment ofthe present invention.

FIGS. 24A to 24E are cross-sectional views showing the processes of amethod producing the photomask of the fourth embodiment of the presentinvention. FIG. 24F is a plan view corresponding to the cross-sectionalview of FIG. 24C, and FIG. 24G is a plan view corresponding to thecross-sectional view of FIG. 24E.

FIGS. 25A to 25C are diagrams illustrating an influence of a phasechange due to a light-shielding portion with a reduced thickness beingused as the semi-light-shielding portion of the photomask of the fourthembodiment on the pattern formation.

FIG. 26A is a plan view of the photomask of the fourth embodiment of thepresent invention in which a dug portion in a transparent substrate isapart from an opening by a predetermined distance. FIGS. 26B to 26D arecross-sectional views in this case.

FIGS. 27A to 27G are diagrams illustrating the image enhancementprinciple with a conventional half-tone phase-shifting mask.

DETAILED DESCRIPTION OF THE INVENTION

First, a method for improving the resolution with the photomask inventedby the inventors of the present application to realize the presentinvention, more specifically, an “outline enhancement method” to improvethe resolution of isolated space patterns will be described below.

Outline Enhancement Method

Hereinafter, the outline enhancement method will be described by takingformation of contact patterns by a positive resist process as anexample. The “outline enhancement method” is a principle that can beused for any patterns, regardless of its shape, as long as the patternsare small space patterns in a positive resist process. Furthermore, the“outline enhancement method” can be applied to a negative resist processtotally in the same manner, if the small space patterns (resist-removedpatterns) in the positive resist process are replaced by small patterns(resist patterns).

FIGS. 1A to 1G are diagrams illustrating the principle to enhance thecontract of transferred images of light in exposure for forming contactpatterns.

FIG. 1A is a plan view of a photomask in which an opening (i.e.,light-transmitting portion) corresponding to a contact pattern issurrounded by a semi-light-shielding portion having a transmittance of6% or more and 15% or less with respect to exposure light. FIG. 1B showsthe amplitude intensity corresponding to line AA′ of light transmittedthrough the photomask shown in FIG. 1A.

FIG. 1C is a plan view of a photomask in which a phase shifter isdisposed in a peripheral area of the opening shown in FIG. 1A, and acomplete light-shielding portion is disposed in the other area FIG. 1Dshows the amplitude intensity corresponding to line AA′ of lighttransmitted through the photomask shown in FIG. 1C. The amplitudeintensity of light shown in FIG. 1D is that of the light transmittedthrough a-phase shifter, and therefore this amplitude intensity has anopposite phase with respect to the amplitude intensity of light shown inFIG. 113.

FIG. 1E is a plan view of a photomask in which an opening correspondingto a contact pattern and a phase shifter disposed in the peripheral areaof the opening are surrounded by a semi-light-shielding portion having atransmittance of 6% or more and 15% or less with respect to exposurelight. FIGS. 1F and 1G are the amplitude intensity and the lightintensity (a square of the amplitude intensity of light) correspondingto line AA′ of light transmitted through the photomask shown in FIG. 1E.The photomask shown in FIG. 1E is a photomask obtained by disposing aphase shifter in a peripheral area of the opening in the photomask shownin FIG. 1A. The photomask shown in FIG. 1E is an example of thephotomask of the present invention that can realize the outlineenhancement method (hereinafter, referred to as “outline enhancementmask”).

The photomask shown in FIG. 1A or 1E, the light transmitted through thesemi-light shielding portion and the light transmitted through theopening have the same phase (more specifically, a phase difference of(−30+360×n) degrees or more and (30+360×n) degrees or less, where n=aninteger). In the photomask shown in FIG. 1E, the light transmittedthrough the phase shifter and the light transmitted through the openinghave opposite phases (more specifically, a phase difference of(150+360×n) degrees or more and (210+360×n) degrees or less, where n=aninteger).

The principle based on which transferred image of light transmittedthrough the outline enhancement mask shown in FIG. 1E is as follows. Thestructure of the photomask shown in FIG. 1E is a structure in which thephotomasks shown in FIGS. 1A and 1C are overlapped each other.Therefore, as shown in FIGS. 1B, 1D, and 1F, the amplitude intensity oflight transmitted through the photomask shown in FIG. 1E has adistribution similar to that obtained by overlapping the amplitudeintensities of the lights transmitted through the photomasks shown inFIGS. 1A and 1C. As seen from FIG. 1F, in the photomask shown in FIG.1E, if the intensity of light transmitted through the phase shifterdisposed in the periphery of the opening can cancel a part of each ofthe lights transmitted through the opening and the semi-light shieldingportion. Therefore, in the photomask shown in FIG. 1E, if the intensityof the light transmitted through the phase shifter is adjusted such thatlight in the periphery of the opening is canceled, it is possible toform a light intensity distribution in which the light intensitycorresponding to the periphery of the opening is reduced to nearly 0, asshown in FIG. 1G.

In the photomask shown in FIG. 1E, the light transmitted through thephase shifter cancels the light in the periphery of the opening to ahigh degree, but cancels the light in the vicinity of the center of theopening to a low degree. As a result, there is another advantage thatthe slope of the profile of the light intensity distribution of thelight transmitted through the photomask shown in FIG. 1E in which thelight intensity changes from the center of the opening to the peripheryof the opening is increased, as shown in FIG. 1G. Therefore, the lightintensity distribution of the light transmitted through the photomaskshown in FIG. 1E has a sharp profile, so that images having a highcontrast can be formed.

Above described is the principle based on which optical images (imagesof light intensity) in the present invention are enhanced. In otherwords, a phase shifter is disposed along the outline of an opening in amask formed of a semi-light shielding portion having a lowtransmittance, so that it is possible to form a very dark portioncorresponding to the outline of the opening in a light intensity imageformed with the photomask shown in FIG. 1A. Thus, a light intensitydistribution in which the contrast between the light intensity in theopening and the light intensity in the periphery of the opening isenhanced can be formed. In this specification, a method by which imageenhancement is performed based on this principle is referred to as the“outline enhancement method”, and the photomask that realizes thisprinciple is referred to as an “outline enhancement mask”.

Hereinafter, the difference between the outline enhancement method,which is the basic principle of the present invention, and the principleof a conventional method using a half-tone phase-shifting mask will bedescribed. The most important point of the principle of the outlineenhancement mask is that a part of the light transmitted through each ofthe semi-light shielding portion and the opening is canceled by thelight transmitted through the phase shifter, so that a dark portion isformed in the light intensity distribution, that is, that the phaseshifter behaves in a manner similar to a non-transparent pattern (opaquepattern). Therefore, as shown in FIG. 1F, a dark portion is formed by achange in intensity on the same phase side in the amplitude intensity ofthe light transmitted through the outline enhancement mask. Only in thisstate, the contrast can be improved by oblique incident exposure, whichwill be described in detail later.

On the other hand, also in the light intensity distribution obtained byexposure with the conventional half-tone phase-shifting mask having anopening corresponding to a contact pattern, a very dark portion isformed in the periphery of the opening, as shown in FIG. 27G. However,when the amplitude intensity of the light shown in FIG. 27F obtained byexposure with the half-tone phase-shifting mask is compared with theamplitude intensity of the light shown in FIG. 1F obtained by exposurewith the outline enhancement mask, the following difference is clearlypresent. As shown in FIG. 27F, in the amplitude intensity distributionobtained by exposure with the half-tone phase-shifting mask, a phaseboundary in which a phase inversion occurs is present. As shown in FIG.27G, this phase boundary constitutes a dark portion of the lightintensity distribution due to the phase end and thus image enhancementis realized. However, in order to form a dark portion due to the phaseend to obtain an enhancement effect of the contract, a component oflight incident vertically to the photomask is required. On the otherhand, oblique incident exposure cannot provide a dark portion due to aphase end, even if the phase boundary is generated, and consequently thecontrast enhancement effect cannot be obtained. This is the reason whythe contrast enhancement effect cannot be obtained when oblique incidentexposure is performed with the half-tone phase-shifting mask. In otherwords, in order to obtain the contrast enhancement effect with thehalf-tone phase-shifting mask, it is necessary to perform exposure usinga small light source having a low coherence degree.

As described above, in forming contact patterns, although the lightintensity distribution with the half-tone phase-shifting mask is similarto that with the outline enhancement mask, the outline enhancementmethod can provide a higher contrast to a transferred image of light,which is necessary for forming small isolated space patterns, even withoblique incident exposure, because of the difference in the principlefor formation of a dark portion (the phase boundary is not generated inthe amplitude intensity distribution of the light transmitted throughthe outline enhancement mask (see FIG. 1F).

FIG. 2A is a plan view of a half-tone phase-shifting mask in which anopening corresponding to a contact pattern is surrounded by a phaseshifter. FIG. 2B shows calculation results of the light intensitydistribution corresponding to line AA′ when exposure is performed with asmall light source having a small coherence degree a =0.4 with respectto the half-tone phase-shifting mask shown in FIG. 2A. FIG. 2C showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with annular illumination, which isone type of oblique incident exposure, with respect to the half-tonephase-shifting mask shown in FIG. 2A. In this case, what is called 2/3annular illumination having an outer diameter a of 0.75 and an innerdiameter ay of 0.5 is used as the annular illumination. For the exposureconditions, the light source wavelength λ is 193 nm (ArF light source)and the numerical aperture NA is 0.6. The contact size is 180 nm square,and the transmittance of the phase shifter is 6%. In the followingdescription, the light intensity is shown by a relative light intensitywhen taking the light intensity of exposure light as 1, unless otherwisespecified.

As shown in FIGS. 2B and 2C, when the half-tone phase-shifting mask isused, a dark portion due to a phase end is formed in the light intensitydistribution from exposure with a small light source and an image havinga high contrast can be formed. On the other hand, in the light intensitydistribution from oblique incident exposure, a dark portion due to aphase end is not formed, and therefore an image having a very poorcontrast is formed.

FIG. 2D is a plan view of an edge enhancement phase-shifting mask inwhich an opening corresponding to a contact pattern and a phase shifterpositioned in an area surrounding the opening are surrounded by achromium film serving as a complete light-shielding portion. FIG. 2Eshows calculation results of the light intensity distributioncorresponding to line AA′ when exposure is performed with a small lightsource having a small coherence degree σ=0.4 with respect to the edgeenhancement phase-shifting mask shown in FIG. 2D. FIG. 2F showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with annular illumination withrespect to the edge enhancement phase-shifting mask shown in FIG. 2E.Herein, similarly to the half-tone phase-shifting mask, the “edgeenhancement phase-shifting mask” is a mask that can realize imageenhancement by forming a dark portion due to a phase end between anopening and a phase shifter. The type of annular illumination, theexposure conditions and the transmission of the phase shifter are thesame as those in the case of the half-tone phase-shifting mask shown inFIGS. 2A to 2C. The contact size is 220 nm square, and the width of thephase shifter is 80 nm.

As shown in FIGS. 2E and 2F, when the edge enhancement phase-shiftingmask is used, similarly to the case of the half-tone phase-shiftingmask, a dark portion due to a phase end is formed in the light intensitydistribution from exposure with a small light source, and an imagehaving a high contrast can be formed. On the other hand, in the lightintensity distribution from oblique incident exposure, a dark portiondue to a phase end is not formed, and therefore an image having a verypoor contrast is formed.

Next, in the outline enhancement method, before showing in detail thatoblique incident exposure components can provide high contrast, the factthat the structure of the outline enhancement mask as shown in FIG. 1Ecannot provide the outline enhancement effect when the width of thephase shifter becomes too large will be described.

FIG. 3A is a plan view of an outline enhancement mask in which anopening corresponding to a contact pattern and a phase shifter having asmall width positioned in an area surrounding the opening are surroundedby a semi-light shielding portion having a transmittance of 6% or moreand 15% or less with respect to exposure light. FIG. 3B showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with a small light source having asmall coherence σ degree =0.4 with respect to the outline enhancementmask shown in FIG. 3A. FIG. 3C shows calculation results of the lightintensity distribution corresponding to line AA′ when exposure isperformed with annular illumination with respect to the outlineenhancement mask shown in FIG. 3A.

FIG. 3D is a plan view of an outline enhancement mask in which anopening corresponding to a contact pattern and a phase shifter having alarge width positioned in an area surrounding the opening are surroundedby a semi-light shielding portion having a transmittance of 6% or moreand 15% or less with respect to exposure light. FIG. 3E showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with a small light source having asmall coherence degree σ=0.4 with respect to the outline enhancementmask shown in FIG. 3D. FIG. 3F shows calculation results of the lightintensity distribution corresponding to line AA′ when exposure isperformed with annular illumination with respect to the outlineenhancement mask shown in FIG. 3D.

In this case, it is assumed that the width of the phase shifter in theoutline enhancement mask shown in FIG. 3D is set to be too large tosatisfy the principle of the outline enhancement method. Morespecifically, the sizes of the openings shown in FIGS. 3A and 3D areboth 220 nm square, and the width of the phase shifter shown in FIG. 3Ais 60 nm and the width of the phase shifter shown in FIG. 3D is 150 nm.The types of the annular illumination and the exposure conditions arethe same as those in the case of the half-tone phase-shifting mask shownin FIGS. 2A to 2C.

As shown in FIGS. 3B and 3C, when the outline enhancement mask shown inFIG. 3A that satisfies the principle of the outline enhancement methodis used, a dark portion due to a non-transparent function of the phaseshifter appears regardless of the type of the light source and thecontrast in the light intensity distribution is higher in the annularillumination.

On the other hand, when the outline enhancement mask shown in FIG. 3Dwith an excessively large phase shifter is used, the light transmittedthrough the phase shifter is too strong, so that an amplitude intensitydistribution having an opposite phase is formed. In this situation, thesame principle as in the case of the half-tone phase-shifting mask orthe edge enhancement phase-shifting mask acts. In other words, as shownin FIGS. 3E and 3F, a dark portion due to a phase end is formed in thelight intensity distribution obtained by exposure with a small lightsource and the contrast enhancement effect is provided, whereas no darkportion due to a phase end is formed in the light intensity distributionobtained by oblique incident exposure, so that an image having very poorcontrast is formed.

In other words; in order to realize the outline enhancement method, inthe mask structure, it is necessary that not only the phase shifter isdisposed in the periphery of the opening surrounded by the semi-lightshielding portion, but also that the light transmitted through the phaseshifter is limited. According to the mechanism of the principle, thelatter means that the light transmitted through the phase shifter has anintensity that at least can cancel the lights transmitted through thesemi-light shielding portion and the opening, and the intensitydistribution having an opposite phase with a predetermined size or moreis not formed in its amplitude intensity distribution.

In order to actually limit the light transmitted through the phaseshifter, a condition (more specifically the upper limit) can be imposedon the width of the phase shifter, depending on the transmittance of thephase shifter. Hereinafter, the condition will be described withreference to the results of observing conditions under which the lightfrom the periphery of the phase shifter is cancelled by the lighttransmitted through the phase shifter (see FIGS. 4A and 4B).

As shown in FIG. 4A, in exposure with a photomask (phase shifter mask)in which a phase shifter having a transmittance T and a line width L isprovided on a transparent substrate is used, the light intensitygenerated in a position corresponding to the center of the phase shifterin an exposed material is expressed as Ih (L, T). In exposure with aphotomask (light-shielding mask) in which the phase shifter of thephase-shifting mask is replaced by a complete light-shielding portion isused, the light intensity generated in a position corresponding to thecenter of the complete light-shielding portion in an exposed material isexpressed as Ic (L). In exposure with a photomask (light-transmittingmask) in which the phase shifter of the phase-shifting mask is replacedby an opening (light-transmitting portion) and the light-transmittingportion of the phase-shifting mask is replaced by a completelight-shielding portion is used, the light intensity generated in aposition corresponding to the center of the opening in an exposedmaterial is expressed as Io (L).

FIG. 4B is a graph showing the simulation results of the light intensityIh (L, T) when the transmittance T and the line width L of the phaseshifter are varied in exposure with the phase-shifting mask shown inFIG. 4A, represented by contour lines of the light intensity with thetransmittance T and the line width L in the vertical axis and thehorizontal axis, respectively. In this graph, a graph indicating therelationship of T=Ic (L)/Io (L) is superimposed The simulationconditions are such that the wavelength of the exposure light λ=0.193μm(ArF light source), the numerical aperture NA of the projection opticalsystem of the exposure apparatus =0.6, and the coherence degree a of theexposure light source =0.8 (regular light source).

As shown in FIG. 4B, the condition under which the light intensity Ih(L, T) becomes smallest can be expressed by a relationship T=Ic(L)/Io(L). This physically represents a relationship in which T×Io (L)indicating the light intensity of the light transmitted through thephase shifter is in equilibrium with Ic (L) indicating the lightintensity of the light transmitted outside the phase shifter. Therefore,the width L of the phase shifter that provides an amplitude intensity ofan opposite phase in the amplitude intensity distribution because ofexcessive light transmitted through the phase shifter is a width L thatallows T×Io(L) to be larger than Ic (L).

It is empirically obtained from various simulation results that thewidth L that allows the light transmitted through the phase shifterhaving a transmittance of 1 to be in equilibrium with the lighttransmitted outside the phase shifter is about 0.3×λ(light sourcewavelength)/NA (numerical aperture) (about 100 nm in the case of FIG.4B), although this may depend on the type of the light source.Furthermore, as seen from FIG. 4B, in order to prevent too much lightfrom being transmitted through the phase shifter having a transmittanceof 6% (0.06) or more, the width L should be not more than twice thewidth of the phase shifter having a transmittance of 100% (1.0). That isto say, in order to prevent too much light from being transmittedthrough the phase shifter having a transmittance of 6% or more, theupper limit of the width L of the phase shifter should be not more than0.6×λ/NA.

If the above-described findings are applied to the outline enhancementmask, the upper limit of the width L of the phase shifter in the outlineenhancement mask can be considered to be a half of the upper limit inthe above findings because the light transmitted outside the phaseshifter in the outline enhancement mask to be taken into considerationis significantly only light on one side rather than both sides of thephase shifter. Therefore, the upper limit of the width L of the phaseshifter in the outline enhancement mask is not more than 0.3×λ/NA whenthe transmittance of the phase shifter is 6% or more. However, this isnot a sufficient condition, and the upper limit of the width L of thephase should be smaller than 0.3×λ/NA, depending on how high thetransmittance of the phase shifter is. That is to say, when thetransmittance of the phase shifter is as high as 100% or 50% or more,the width L of the phase shifter should be 0.2×λ/NA or less, preferably0.15 ×λ/NA or less. When forming fine hole patterns, in order to obtainthe effect of enhancing the profile of the light intensity distributionby interference between the light transmitted though the phase shifterand the light transmitted through the light-transmitting portioncorresponding to a hole pattern, it is preferable to arrange the phaseshifter in a region with a distance from the center of thelight-transmitting portion, that is, the hole of 0.5×λ/NA or less.Therefore, when the width L of the phase shifter is 0.3×λ/NA or less, itis preferable in forming hole patterns that the phase shiftersurrounding the light-transmitting portion is present in a region with adistance from the center of the light- transmitting portioncorresponding to the hole pattern of 0.5×λNA or more and 0.8×λ/NA orless.

In this specification, unless otherwise specified, various mask sizessuch as the width of a phase shifter are shown by the sizes on anexposed material. The actual mask size can be obtained easily bymultiplying the sizes on an exposed material by the reduction ratio M ofa reduction projection optical system of an exposure apparatus.

Next, the image enhancement that can be realized with oblique incidentexposure in the outline enhancement method will be described in detail,based on a change in the contrast of the light intensity distributionwhen exposure is performed from various light source positions withrespect to the outline enhancement mask.

FIG. 5A is a plan view of the outline enhancement mask. In this case,the transmittance of the semi-light-shielding portion is 7.5%, and thetransmittance of the phase shifter and the opening is 100%. The size ofthe opening is 200 nm square, and the width of the phase shifter is 50nm.

FIG. 5C shows the results obtained by calculating the light intensitydistribution corresponding to line AA′ of FIG. 5A when exposure isperformed from a point light source in various positions normalized withthe numerical aperture NA with respect to the outline enhancement maskshown in FIG. 5A with optical simulations, reading the light intensityIo in a position corresponding to the center of the opening in thecalculation results (e.g., the light intensity distribution shown inFIG. 5B) and plotting the light intensity Io against each light sourceposition. The results shown in this plot are from the opticalcalculations that are performed assuming that the light sourcewavelength λ is 193 nm (ArF light source) and the numerical aperture NAis 0.6. In the following description, unless otherwise specified, in theoptical simulations, a calculation is performed under the conditionsthat the light source wavelength λ is 193 nm (ArF light source) and thenumerical aperture NA is 0.6.

As shown in FIG. 5C, the light intensity Io in the center of the openingis larger, as exposure is performed with a point light source in a lightposition on the outer side (a light source position more apart from theorigin in FIG. 5C). That is to say, the plot shows that as exposure isperformed with a light source having a larger oblique incidentcomponent, the contrast is larger. This will be described morespecifically with reference to the drawings. FIGS. 5D, 5E, and 5F aregraphs obtained by plotting the light intensity distributioncorresponding to line AA′ of FIG. 5A in sample points P1, P2 and P3 ofthe point light sources shown in FIG. 5C, respectively. As shown inFIGS. 5D, 5E, and 5F, as the position of the point light source is onthe outer side, in other words, as the light source is in the positionthat provides larger oblique incident light, an image of a highercontrast is formed.

Next, for comparison, a change in the contrast of the light intensitydistribution when exposure is performed from various light sourcepositions with respect to the half-tone phase-shifting mask will bedescribed. FIG. 6A is a plan view of the half-tone phase-shifting mask.In this case, the transmittance of the phase shifter is 6%, and thetransmittance of the opening is 100%. The size of the opening (size onan exposed wafer) is 180 nm square.

FIG. 6C shows the results obtained by calculating the light intensitydistribution corresponding to line AA′ of FIG. 6A when exposure isperformed from a point light source in various positions normalized withthe numerical aperture NA with respect to the half-tone phase-shiftingmask shown in FIG. 6A with optical simulations, reading the lightintensity Io in a position corresponding to the center of the opening inthe calculation results (e.g., the light intensity distribution shown inFIG. 6B) and plotting the light intensity Io against each light sourceposition.

As shown in FIG. 6C, the light intensity Io in the center of the openingis larger, as exposure is performed with a point light source in a lightposition on the inner side (a light source position closer to the originin FIG. 6C). That is to say, the plot shows that as exposure isperformed with a light source having a larger vertical incidentcomponent, the contrast is larger. This will be described morespecifically with reference to the drawings. FIGS. 6D, 6E, and 6F aregraphs obtained by plotting the light intensity distributioncorresponding to line AA′ of FIG. 6A in sample points P1, P2 and P3 ofthe point light sources shown in FIG. 6C, respectively. As shown inFIGS. 6D, 6E, and 6F, as the position of the point light source is onthe inner side, in other words, as the light source is in the positionthat provides larger vertical incident light, an image of a highercontrast is formed.

As seen from the comparison between the results shown in FIGS. 5A to 5Fand the results shown in FIGS. 6A to 6F, the outline enhancement methodmakes it possible to enhance the contrast of the light intensitydistribution obtained by oblique incident exposure in forming smallisolated space patterns such as contact patterns, which cannot berealized by the conventional methods.

The fact that the contrast is improved by the outline enhancement maskhas been described so far. Next, the dependence of the contrast and theDOF on the transmittance of the semi-light-shielding portion in theoutline enhancement mask will be described below. The followingdescription is based on the results obtained by simulations of variousmargins in pattern formation, using the outline enhancement mask shownin FIG. 7A. FIG. 7B shows the light intensity distribution formed whenexposure is performed with respect to the outline enhancement mask shownin FIG. 7A. In FIG. 7B, values regarding various margins defined whenforming a hole pattern with a width of 100 nm using the outlineenhancement mask shown in FIG. 7A are also shown. More specifically, thecritical intensity Ith is the light intensity that allows a resist filmto be exposed, and the margin is defined with respect to this value. Forexample, if Ip is the peak value of the light intensity distribution,Ip/Ith is proportional to the sensitivity with which a resist mask isexposed, and the higher value is more preferable. If Ib is thebackground intensity of light transmitted through thesemi-light-shielding portion, a higher Ith/Ib means that a reduction inthickness of the resist film hardly occurs at pattern formation, and thehigher value is more preferable. In general, it is preferable that avalue of Ith/Ib is at least 2. With the foregoing in mind, each marginwill be described.

FIG. 7C shows the calculation results regarding the dependence of theDOF on the transmittance of a semi-light-shielding portion in patternformation using the outline enhancement mask shown in FIG. 7A. Here, theDOF is defined as the width of the focus position in which a change inthe size of a finished pattern is within 10%. As shown in FIG. 7C, thehigher transmittance the semi-light-shielding portion has, the morepreferable it is for improvement of the DOF. FIG. 7D shows thecalculation results regarding the peak value Ip with respect to thetransmittance of the semi-light shielding portion in pattern formationusing the outline enhancement mask shown in FIG. 7A. As shown in FIG.7D, the higher transmittance the semi-light-shielding portion has, themore preferable it is for improvement of the peak value Ip, that is, thecontrast as well. From the above-described results, in the outlineenhancement mask, the higher transmittance the semi-light-shieldingportion has, the more preferable it is. More specifically, as shown inFIGS. 7C and 7D, the improvement rate of the exposure margin isincreased with an increase of the transmittance from 0% to about 6% andit can be appreciated that it is preferable to use asemi-light-shielding portion having a transmittance of about 6% or more.

FIG. 7E shows the calculation results regarding the Ith/Ib with respectto the transmittance of the semi-light shielding portion in patternformation using the outline enhancement mask shown in FIG. 7A. As shownin FIG. 7E, the higher transmittance the semi-light-shielding portionhas, the lower the value of Ith/Ib is. It is not preferable forimprovement of Ith/Ib that the transmittance is too high. Morespecifically, Ith/Ib is less. than 2 when the transmittance of thesemi-light-shielding portion is about 15%. FIG. 7F shows the calculationresults regarding the Ip/Ith with respect to the transmittance of thesemi-light shielding portion in pattern formation using the outlineenhancement mask shown in FIG. 7A. As shown in FIG. 7F, the Ip/Ith has apeak at a transmittance of about 15% of the semi-light-shieldingportion.

As described above, in the outline enhancement mask, the DOF and thecontrast are improved more, as the transmittance of thesemi-light-shielding portion is higher, and this effect is moresignificant when the transmittance of the semi-light-shielding portionexceeds 6%. On the other hand, to prevent a reduction in thickness ofthe resist film during pattern formation or to optimize the resistsensitivity, it is preferable that the maximum of the transmittance ofthe semi-light-shielding portion is about 15%. Therefore, the optimalvalue of the transmittance of the semi-light-shielding portion in theoutline enhancement mask is 6% or more and 15% or less. That is to say,the semi-light-shielding portion transmits exposure light partially toan extent that the resist is not exposed. In other words, thesemi-light-shielding portion transmits a part of the total amount ofexposure light. Such a semi-light-shielding portion can be formed ofoxides such as ZrSiO, CrAlO, TaSiO, MoSiO or TiSiO.

FIGS. 8A to 8F are plan views showing variations of a light shieldingmask patterns constituted by a semi-light shielding portion and a phaseshifter in the outline enhancement mask provided with an openingcorresponding to a contact pattern.

An outline enhancement mask 1a shown in FIG. 8A has the same structureof that of the outline enhancement mask shown in FIG. 1E. That is, theoutline enhancement mask 1 a is a photomask using a transparentsubstrate 2 a and includes a semi-light-shielding portion 3 a having atransmittance that allows a part of exposure light to be transmitted, anopening 4 a surrounded by the semi-light-shielding portion 3 a andcorresponding to an isolated contact pattern, and a ring-shaped phaseshifter 5 a positioned around the opening 4 a.

The outline enhancement mask 1 b shown in FIG. 8B is a photomask using atransparent substrate 2 b and includes a semi-light-shielding portion 3b having a transmittance that allows a part of exposure light to betransmitted, an opening 4 b surrounded by the semi-light-shieldingportion 3 b and corresponding to an isolated contact pattern, and aphase shifter 5 b constituted by four rectangular phase shifter portionsthat have a side having the same length of each side of the opening 4 band are in contact with the respective sides of the opening 4 b. Thisoutline enhancement mask 1 b has substantially the same characteristicsas those of the outline enhancement mask 1 a in isolated patternformation.

The outline enhancement mask 1 c shown in FIG. 8C is a photomask using atransparent substrate 2 c and includes a semi-light-shielding portion 3c having a transmittance that allows a part of exposure light to betransmitted, an opening 4 c surrounded by the semi-light-shieldingportion 3 c and corresponding to an isolated contact pattern, and aphase shifter 5 c constituted by four rectangular phase shifter portionsthat have a side having a length smaller than each side of the opening 4c and are in contact with the respective sides of the opening 4 c. Thecenter of each phase shifter portion of the phase shifter 5 c is alignedwith the center of the respective side of the opening 4 c. In thisoutline enhancement mask 1 c, the size of the resist pattern to beformed after exposure can be adjusted by changing the length of eachphase shifter portion of the phase shifter 5 c with the width (size) ofthe opening 4 c unchanged. For example, as the length of each phaseshifter portion of the phase shifter 5 c is smaller, the size of theresist pattern becomes larger. In this case, the lower limit withinwhich the length of each phase shifter portion of the phase shifter 5 ccan be changed without losing the function of outline enhancement islimited to about a half of the wavelength of the light source (exposurelight). On the other hand, since the pattern size is changed only to anextent of about a half of the change amount of the mask size, adjustingthe length of the phase shifter portion is an excellent approach toadjust the pattern size.

The outline enhancement mask 1 d shown in FIG. 8D is a photomask using atransparent substrate 2 d and includes a semi-light-shielding portion 3d having a transmittance that allows a part of exposure light to betransmitted, an opening 4 d surrounded by the semi-light-shieldingportion 3 d and corresponding to an isolated contact pattern, and aring-shaped phase shifter 5 d positioned apart from the boundary of thesemi-light-shielding portion 3 d and the opening 4 d by a predetermineddistance on the side of the semi-light-shielding portion 3 d. That is tosay, a ring-shaped semi-light-shielding portion 3 d is present betweenthe phase shifter 5 d and the opening 4 d.

The outline enhancement mask 1 e shown in FIG. 8E is a photomask using atransparent substrate 2 e and includes a semi-light-shielding portion 3e having a transmittance that allows a part of exposure light to betransmitted, an opening 4 e surrounded by the semi-light-shieldingportion 3 e and corresponding to an isolated contact pattern, and aphase shifter 5 e positioned apart from the boundary of thesemi-light-shielding portion 3 e and the opening 4 e by a predetermineddistance on the side of the semi-light-shielding -portion 3 e. The phaseshifter 5 e is constituted by four phase shifter portions, each of whichis a rectangular shape having a length larger than each side of theopening 4 e and whose corner is in contact with the corners of theadjacent portions on the diagonal line of the opening 4 e. In this case,a ring-shaped semi-light-shielding portion 3 e is present between thephase shifter 5 e and the opening 4 e. In this outline enhancement mask1 e, the size of the resist pattern to be formed after exposure can beadjusted by changing only the width (size) of the opening 4 e with thesize and the arrangement of the phase shifter 5 e with unchanged. Forexample, as the width of the opening 4 e is increased, the size of theresist pattern is increased. According to this approach of adjusting thepattern size by changing only the width of the opening, MEEF (Mask ErrorEnhancement Factor: the ratio of the change amount of the pattern sizewith respect to the change amount of the mask size) is reduced to abouta half of that obtained by an approach of scaling both the opening andthe phase shifter at the same time to adjust the pattern size.

The outline enhancement mask if shown in FIG. 8F is a photomask using atransparent substrate 2 f and includes a semi-light-shielding portion 3f having a transmittance that allows a part of exposure light to betransmitted, an opening 4 f surrounded by the semi-light-shieldingportion 3 f and corresponding to an isolated contact pattern, and aphase shifter 5 f positioned apart from the boundary of thesemi-light-shielding portion 3 f and the opening 4 f by a predetermineddistance on the side of the semi-light-shielding portion 3 f. The phaseshifter 5 f is constituted by four phase shifter portions, each of whichis a rectangular shape having the same length as that of each side ofthe opening 4 f and whose side is opposed to the corresponding side ofthe opening 4 f. In this case, the length of each phase shifter portionof the phase shifter 5 f may be larger or smaller than that of the sideof the opening 4 f. According to this outline enhancement mask if, thesize of the resist pattern can be adjusted as in the case of the outlineenhancement mask 1 c shown in FIG. 8C.

In the outline enhancement masks shown in FIGS. 8D to 8F, in order toincrease the effect of reducing the MEEF, it is preferable that thewidth of the semi-light-shielding portion between the opening and thephase shifter is about ⅕ of λ/NA (λ is the wavelength of the exposurelight and NA is the numerical aperture). In order to obtain the effectof improving the DOF, it is preferable that the width of thesemi-light-shielding portion is a size that allows an interferenceeffect of light by the phase shifter to be provided, that is, about 1/10of?/NA or less. In the outline enhancement masks shown in FIGS. 8A to8F, a square is used as the shape of the opening. However, a polygonsuch as an octagon or a circle, or other shapes can be used. The shapeof the phase shifter is not limited to a continuous ring shape or aplurality of rectangles. For example, the phase shifter can be formed byaligning a plurality of square phase shifter portions.

All the above description has been based on the positive resist processin which the portion corresponding to a resist-removed portion in theoutline enhancement mask is defined as the opening. However, if a phaseshifter having a sufficiently high transmittance can be used, in theoutline enhancement mask used for the above description, the portiondefined as the opening can be replaced by a phase shifter having a hightransmittance, the portion defined as the phase shifter can be replacedby an opening, and the portion defined as the semi-light-shieldingportion can be replaced by a phase shifter having a low transmittance(e.g., a phase shifter of a half-tone phase-shifting mask). In thiscase, the relationship of the relative phase difference between theelements is the same as in the above-described case, so that an outlineenhancement mask having the same effect can be realized.

First Embodiment

Hereinafter, a photomask according to a first embodiment of the presentinvention, a method for producing the photomask and a method for forminga pattern using the photomask will be described with reference to theaccompanying drawings. The photomask of the first embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

FIG. 9A shows an example of a desired pattern to be formed with thephotomask of the first embodiment.

When the reduction ratio of a reduction projection optical system of anexposure apparatus is M, in a regular photomask, a pattern having a sizeM times the size of a desired. pattern (in general, having a designedvalue on a wafer) is drawn on a substrate (transparent substrate) formedof a material having a high transmittance with respect to exposurelight, using a material, such as chromium film serving as a completelight-shielding portion with respect to the exposure light. However, inthis specification, for simplification, the present invention isdescribed, using the size on a wafer rather than using the size on themask, which is a size M times the size on a wafer, unless otherwisespecified. In this embodiment, when describing pattern formation, thedescription is based on the positive resist process, unless otherwisespecified. That is to say, the description is based on the assumptionthat an exposed portion of the resist film is removed. On the otherhand, when a negative resist process is assumed to be used, thedescription is totally the same as in the case of the positive resistprocess, except that the exposed portion of the resist film becomes aresist pattern. In this embodiment, the transmittance is expressed by aneffective transmittance when the transmittance of the transparentsubstrate is taken as 100%, unless otherwise specified.

FIG. 9B is a plan view of the photomask of the first embodiment, morespecifically, a photomask for forming the desired pattern shown in FIG.9A. As shown in FIG. 9B, openings (light-transmitting portions) areprovided so as to correspond to resist-removed portions in the desiredpattern. Furthermore, a semi-light-shielding portion having a lowtransmittance (about 6 to 15%) that does not allow the resist film to beexposed and transmits exposure light in the same phase as that of theopening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. In the first embodiment, the transmittance ofthe semi-light-shielding portion is set to, for example, 7.5%. Phaseshifters (peripheral portions) that transmit exposure light in a phaseopposite to that of the opening are provided in the periphery of theopenings. In this embodiment, the transmittance of the phase shifters isset to a higher value than that of the semi-light-shielding portion, forexample, 20% so that the light transmitted through the phase-shifter cancancel the lights transmitted through the openings and thesemi-light-shielding portions effectively, according to the principle ofthe outline enhancement method.

In the first embodiment, for example, as shown in FIG. 8B, the phaseshifters are arranged in such a manner that the sides of the phaseshifters are in contact with the corresponding sides of the rectangularopening in a region having a predetermine size or less from each side ofthe rectangular opening.

FIG. 9C is a cross-sectional view taken along line AA′ in FIG. 9B, thatis a cross-sectional view of the photomask of the first embodiment. Asshown in FIG. 9C, the surface of the transparent substrate 10 in theopening (light-transmitting portion) formation region is exposed. Alower phase shift film 11 that transmits exposure light with a phasedifference (opposite phase) of 180 degrees (more specifically(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer)) between this film and the opening is formed on thetransparent substrate 10 in the phase shifter (peripheral portion)formation region. The lower phase shift film 11 and an upper phase shiftfilm 12 that transmits exposure light in a phase opposite to that of theopening are laminated sequentially on the transparent substrate 10 inthe semi-light-shielding portion formation region. As the lower phaseshift film 11 and the upper phase shift film 12, an oxide film such asZrSiO, CrAlO, TaSiO, MoSiO or TiSiO can be used. However, it ispreferable that the lower phase shift film 11 and the upper phase shiftfilm 12 are formed of different oxide films each other. Here, the lowerphase shift film 11 is a phase shift film having a transmittance of 20%as a single film. On the other hand, the structure in which the lowerphase shift film 11 and the upper phase shift film 12 are laminated actsas a semi-light-shielding film that has a transmittance of 7.5% andcauses a phase difference (the same phase) of 360 degrees (morespecifically, (−30+360×n) degrees or more and (30+360×n) degrees orless, (where n=an integer)). In other words, the structure in which thelower phase shift film 11 and the upper phase shift film 12 arelaminated acts as a half-tone film in which phase inversion does notoccur. Furthermore, a peripheral portion, that is, a phase shifterhaving a single layered structure of the lower phase shift film 11 isformed between the semi-light-shielding portion and the opening. Asdescribed above, the photomask of this embodiment acts as an outlineenhancement mask. However, as described above, in order to obtaincontrast enhancement by the outline enhancement method, it is necessaryto limit the width of the phase shifter to a predetermined size or less.

In the above description, as shown in FIG. 10A, it is assumed that thelower phase shift film 11 and the upper phase shift film 12 are each asingle layered film. In this case, the optical constant of each phaseshift film is determined by its material, so that the thickness of eachphase shift film is determined by the amount of the phase shift. On theother hand, the transmittance depends on not only the optical constant,but also the film thickness, so that for the material of the phase shiftfilm, a material having an appropriate optical constant, morespecifically, a material that can achieve exactly a predeterminedtransmittance with a thickness that can transmit exposure light in aphase opposite to that of the opening is not necessarily present.Therefore, in the first embodiment, as shown in FIG. 10B, it ispreferable that the lower phase shift film 11 has a first transmittanceadjusting film 11A and a first phase adjusting film 11B on the firsttransmittance adjusting film 11A, and the upper phase shift film 12 hasa second transmittance adjusting film 12A and a second phase adjustingfilm 12B on the second transmittance adjusting film 12A in order toachieve an arbitrary transmittance in each phase shift film. The firsttransmittance adjusting film 11A and the second transmittance adjustingfilm 12A transmit exposure light in the same phase as that of theopening and have a relatively low transmittance with respect to exposurelight. On the other hand, the first phase adjusting film 11B and thesecond phase adjusting film 12B transmit exposure light in a phaseopposite to that of the opening and have a relatively high transmittancewith respect to exposure light. As the first transmittance adjustingfilm 11A and the second transmittance adjusting film 12A, a thin film(having a thickness of 30 nm or less) made of a metal such as Zr, Cr,Ta, Mo or Ti or a thin film (having a thickness of 30 nm or less) madeof a metal alloy such as a Ta-Cr alloy, a Zr-Si alloy, a Mo-Si alloy ora Ti-Si alloy can be used. As the first phase adjusting film 11B and thesecond phase adjusting film 12B, an oxide film such as SiO₂ film can beused.

In FIG. 1OB, an example in which both the lower phase shift film 11 andthe upper phase shift film 12 have a two layered structure isillustrated, but one of the lower phase shift film 11 and the upperphase shift film 12 may have a two layered structure, and the other mayhave a single layered structure.

In this specification, a transmittance adjusting film refers to a filmthat has relatively a low transmittance per unit thickness with respectto exposure light and can set the transmittance with respect to exposurelight to a desired value by adjusting the thickness without affectingthe phase change with respect to the exposure light. A phase adjustingfilm refers to a film that has relatively a high transmittance per unitthickness with respect to exposure light and can set the phasedifference with respect to exposure light between this film and thetransparent substrate (opening) to a desired value by adjusting thethickness without affecting the transmittance change with respect to theexposure light.

Next, a method for forming a pattern using the photomask of the firstembodiment will be described. As described with reference to theprinciple of the outline enhancement method when transferring a maskpattern in a reduced size with an exposure apparatus, it is preferableto use an oblique incident exposure light source in order to form animage having a high contrast with the outline enhancement mask. Herein,“oblique incident exposure” refers to light sources shown in FIGS. 11Bto 11D in which vertical incident components are removed, as opposed toa regular exposure light source as shown in FIG. 1A. Representativeoblique incident exposure light sources are an annular exposure lightsource shown in FIG. 11B and a quadrupole exposure light source shown inFIG. 11C. Although it depends slightly on a desired pattern, in general,quadrupole exposure light sources are more advantageous in enhancementof the contrast and enlargement of the DOF than annular exposure lightsources. However, quadrupole exposure light sources have such sideeffects that a pattern shape is distorted from the mask shape, so thatin such a case, it is preferable to use an annular-quadrupole mixed typeexposure light source as shown in FIG. 11D. The annular-quadrupole mixedtype exposure light source is characterized by having a feature of aquadrupole light source that the center of the light source and thelight sources on the XY axis are removed when assuming the XY coordinatewith the center of the light source (center of a regular exposure lightsource) as the origin, and having a feature of an annular light sourcethat a circle is used-as the contour of the light source.

FIGS. 12A to 12D are cross-sectional views showing the processes of amethod forming patterns with the photomask of the first embodiment.

First, as shown in FIG. 12A, after a film 101 to be processed such as ametal film or an insulating film is formed on a substrate 100, as shownin FIG. 12B, a positive resist film 102 is formed on the film 101 to beprocessed.

Next, as shown in FIG. 12C, the photomask of the first embodimentincluding a semi-light-shielding portion made of a multilayeredstructure of the lower phase shift film 11 and the upper phase shiftfilm 12 and a phase shifter made of a single layered structure of thelower phase shift film 11 is irradiated with exposure light 103 with anoblique incident exposure light source to expose the resist film 102with transmitted light 104 transmitted through the photomask. In thiscase, a semi-light-shielding portion having a low transmittance is usedas the mask pattern, so that the entire resist film 102 is exposed withweak energy. However, as shown in FIG. 12C, only a latent image portion102 a of the resist film 102 corresponding to the light-transmittingportion (opening) in the photomask is irradiated with the exposureenergy that is sufficient to dissolve the resist film 102 in adeveloping process.

Next, the latent image portion 102 a is removed by performingdevelopment with respect to the resist film 102, so that as shown inFIG. 12D, a resist pattern 105 is formed. In this case, in the exposureprocess shown in FIG. 12C, light in the periphery of the opening iscanceled, so that a portion corresponding to the phase shifter(peripheral portion) in the resist film 102 is substantially notirradiated with exposure energy. Therefore, the contrast in the lightintensity distribution between the light transmitted through the openingand the light transmitted through the peripheral portion, in otherwords, the contrast in the light intensity distribution between thelight with which the latent image portion 102 a is irradiated and thelight with which the periphery of the latent portion 102 a is irradiatedcan be enhanced. Therefore, the energy distribution in the latentportion 102 a is changed sharply, so that a resist pattern 105 having asharp shape can be formed.

Next, a method for producing a photomask of the first embodiment will bedescribed with reference to the drawings.

FIGS. 13A to 13E are cross-sectional views showing the processes of amethod producing the photomask of the first embodiment. FIG. 13F is aplan view corresponding to the cross-sectional view of FIG. 13C, andFIG. 13G is a plan view corresponding to the cross-sectional view ofFIG. 13E.

First, as shown in FIG. 13A, a lower phase shift film 11 made of, forexample, TaSiO and an upper phase shift film 12 made of, for example,MoSiO are formed sequentially on a transparent substrate 10 made of amaterial having light-transmitting properties with respect to exposurelight, such as quartz. As the lower phase shift film 11 and the upperphase shift film 12, an oxide film such as ZrSiO, CrAlO, TaSiO, MoSiO orTiSiO can be used. However, it is preferable that the lower phase shiftfilm 11 and the upper phase shift film 12 are made of different oxideseach other so that the upper phase shift film 12 can be removedselectively from the lower phase shift film 11. Furthermore, the lowerphase shift film 11 and the upper phase shift film 12 each generate aphase difference of (150+360×n) degrees or more and (210+360×n) degreesor less (where n =an integer) with respect to exposure light betweenthese films and the light-transmitting portion (opening) in thetransparent substrate 10. In this embodiment, at least one of the lowerphase shift film 11 and the upper phase shift film 12 may have a twolayered structure of a transmittance adjusting film and a phaseadjusting film as described above.

Next, as shown in FIG. 13B, a first resist pattern 13 that covers thesemi-light-shielding portion formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in each of the opening (light-transmitting portion)formation region and the phase shifter (peripheral portion) formationregion is formed on the transparent substrate 10. Thereafter, the upperphase shift film 12 is etched with the first resist pattern 13 as a maskto pattern the upper phase shift film 12. Then, the first resist pattern13 is removed Thus, as shown in FIGS. 13C and 13F, the portionscorresponding to the opening formation region and the phase shifterformation region in the upper phase shift film 12 are removed.

Next as shown in FIG. 13D, a second resist pattern 14 that covers thesemi-light-shielding portion formation region and the phase shifterformation region is formed on the transparent substrate 10. That is, asecond resist pattern 14 having a removed portion in the openingformation region is formed. Thereafter, the lower phase shift film 11 isetched with the second resist pattern 14 as a mask to pattern the lowerphase shift film 11. Then, the second resist pattern 14 is removed.Thus, as shown in FIGS. 13E and 13G, the portion corresponding to theopening formation region in the lower phase shift film 11 is removed,and thus the photomask of the first embodiment is completed. That is tosay, the photomask of the first embodiment having the plane structure ofthe outline enhancement mask can be easily formed by, as a mask blank,preparing a transparent substrate in which two half-tone phase shiftfilms are deposited, and then performing selective etching with respectto the lower and upper phase shift films sequentially.

As described above, according to the first embodiment, the lower phaseshift film 11 and the upper phase shift film 12 that transmit exposurelight with a phase inversion are formed sequentially on the transparentsubstrate 10. Then, the portions of upper phase shift film 12 in theopening light-transmitting portion) formation region and the phaseshifter (peripheral portion) formation region is removed. Thereafter,the portion of the lower phase shift film 11 in the opening formationregion is removed. That is to say, the opening is made of the exposedportion of the transparent substrate 10, and the semi-light-shieldingportion is made of a multilayered structure of the lower phase shiftfilm 11 and the upper phase shift film 12. The phase shifter is made ofa single layered structure of the lower phase shift film 11. Themultilayered structure of the lower phase shift film 11 and the upperphase shift film 12 transmits exposure light in the same phase as thatof the opening. Therefore, the phase shifter that transmits exposurelight in the phase opposite to that of the opening is sandwiched by theopening and the semi-light-shielding portion that transmits exposurelight in the same phase as that of the opening. As a result, thecontrast in the light intensity distribution between the opening and thephase shifter can be enhanced by mutual interference between the lighttransmitted through the opening and the light transmitted through thephase shifter. This contrast enhancement effect also can be obtainedwhen a fine isolated resist-removed portion (i.e., a fine isolated spacepattern corresponding to the light-transmitting portion) is formed withoblique incident exposure, for example, in the positive resist process.That is to say, it is possible to miniaturize isolated space patternsand isolated line patterns or dense patterns at the same time withoblique incident exposure.

According to the first embodiment, the lower phase shift film 11 and theupper phase shift film 12 that are laminated on the transparentsubstrate 10 are etched selectively, so that a mask pattern with anyshape that has the semi-light-shielding portion and the phase shifter(peripheral portion) can be easily realized.

According to the first embodiment, a phase shifter with any shape can beformed by processing the upper phase shift film 12 of the multilayeredstructure of the lower phase shift film 11 and the upper phase shiftfilm 12 constituting the semi-light-shielding portion. For this reason,as the pattern layout of the outline enhancement mask, not only the typeshown in FIGS. 9B and 9C, that is, the type shown in FIG. 5B, but alsoall the types shown in FIGS. 8A to 8F, for example, can be realized.

According to the first embodiment, the transmittance of the phaseshifter can be defined by the single layered structure of the lowerphase shift film 11, and the transmittance of the semi-light-shieldingportion can be defined by the multilayered structure of the lower phaseshift film 11 and the upper phase shift film 12, so that a combinationof the transmittances of the phase shifter and the semi-light-shieldingportion can be set arbitrarily.

In the first embodiment, it is preferable that the transmittance of thesemi-light-shielding portion (multilayered structure of the lower phaseshift film 11 and the upper phase shift film 12) is 6% or more and 15%or less. Thus, the contrast enhancement effect can be obtained reliablywhile preventing a reduction in thickness of the resist film in patternformation.

In the first embodiment, the description is based on the use of thepositive resist process, but the negative resist process can be used,instead of the positive resist process. In this case, in either one ofthe processes, as the exposure light source, the i line (wavelength 365nm), KrF excimer laser light (wavelength 248 nm), ArF excimer laserlight (wavelength 193 nm), or F₂ excimer laser light (wavelength 157 nm)can be used, for example.

First Variation of the First Embodiment

Hereinafter, a photomask of a first variation of the first embodimentand a method for producing the photomask will be described withreference to the accompanying drawings.

The first variation of the first embodiment is different from the firstembodiment in the following aspects. In the first embodiment, theoutline enhancement mask having a layout in which the phase shifter(peripheral portion) and the opening (light-transmitting portion) areadjacent as shown, for example, in FIGS. 8A to 8C is described. In thefirst variation of the first embodiment, the outline enhancement maskhaving a layout in which the phase shifter and the opening are apart asshown, for example, in FIGS. 8D to 8F is described.

FIGS. 14A to 14E are cross-sectional views showing the processes of amethod producing a photomask of the first variation of the firstembodiment. FIG. 14F is a plan view corresponding to the cross-sectionalview of FIG. 14C, and FIG. 14G is a plan view corresponding to thecross-sectional view of FIG. 14E.

First, as shown in FIG. 14A, a lower phase shift film 11 and an upperphase shift film 12 are formed sequentially on a transparent substrate10 made of a material having light-transmitting properties with respectto exposure light, such as quartz. The lower phase shift film 11 and theupper phase shift film 12 generate a phase difference (opposite phase)of (150+360×n) degrees or more and (210+360×n) degrees or less (wheren=an integer) with respect to exposure light between these films and thelight-transmitting portion (opening) in the transparent substrate 10. Inthis variation, at least one of the lower phase shift film 11 and theupper phase shift film 12 may have a two layered structure of atransmittance adjusting film and a phase adjusting film (see the firstembodiment).

Next, as shown in FIG. 14B, a first resist pattern 13 that covers asemi-light-shielding portion formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in each of an opening (light-transmitting portion)formation region and a phase shifter (peripheral portion) formationregion is formed on the transparent substrate 10. In this variation, theopening formation region and the phase shifter formation region areapart. In other words, the first resist pattern 13 is interposed betweenthe opening formation region and the phase shifter formation region.Thereafter, the upper phase shift film 12 is etched with the firstresist pattern 13 as a mask to pattern the upper phase shift film 12.Then, the first resist pattern 13 is removed. Thus, as shown in FIGS.14C and 14F, the portions corresponding to the opening formation regionand the phase shifter formation region in the upper phase shift film 12are removed.

Next, as shown in FIG. 14D, a second resist pattern 14 that covers thesemi-light-shielding portion formation region including the phaseshifter formation region and that has a removed portion in the openingformation region is formed on the transparent substrate 10. Thereafter,the lower phase shift film 11 is etched with the second resist pattern14 and the patterned upper phase shift film 12 as masks to pattern thelower phase shift film 11. Then, the second resist pattern 14 isremoved. Thus, as shown in FIGS. 14E and 14G, the portion correspondingto the opening formation region in the lower phase shift film 11 isremoved, and thus the photomask of the first variation of the firstembodiment is completed.

According to the first variation of the first embodiment, the followingadvantages can be obtained, in addition to those of the firstembodiment. Since the patterned upper phase shift film 12 is used as amask for etching the lower phase shift film 11 in a self-alignmentmanner, photomask process can be performed precisely.

Second Variation of the First Embodiment

Hereinafter, a photomask of a second variation of the first embodimentand a method for producing the photomask will be described withreference to the accompanying drawings.

The second variation of the first embodiment is different from the firstembodiment in the following aspects. In the first embodiment, theoutline enhancement mask having a layout in which the phase shifter(peripheral portion) and the opening (light-transmitting portion) areadjacent as shown, for example, in FIGS. 8A to 8C is described. In thesecond variation of the first embodiment as well as the first variationof the first embodiment, the outline enhancement mask having a layout inwhich the phase shifter and the opening are apart as shown, for example,in FIGS. 8D to 8F is described.

FIGS. 15A to 15E are cross-sectional views showing the processes of amethod producing a photomask of the second variation of the firstembodiment. FIG. 15F is a plan view corresponding to the cross-sectionalview of FIG. 15C, and FIG. 15G is a plan view corresponding to thecross-sectional view of FIG. 15E.

First, as shown in FIG. 15A, a lower phase shift film 11 and an upperphase shift film 12 are formed sequentially on a transparent substrate10 made of a material having light-transmitting properties with respectto exposure light, such as quartz. The lower phase shift film 11 and theupper phase shift film 12 generate a phase difference (opposite phase)of (150+360×n) degrees or more and (210+360×n) degrees or less (wheren=an integer) with respect to exposure light between these films and thelight-transmitting portion (opening) in the transparent substrate 10. Inthis variation, at least one of the lower phase shift film 11 and theupper phase shift film 12 may have a two layered structure of atransmittance adjusting film and a phase adjusting film (see the firstembodiment).

Next, as shown in FIG. 15B, a first resist pattem 13 that covers asemi-light-shielding portion formation region and an opening(light-transmitting portion) formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in a phase shifter (peripheral portion) formation regionis formed on the transparent substrate 10. Thereafter, the upper phaseshift film 12 is etched with the first resist pattern 13 as a mask topattern the upper phase shift film 12. Then, the first resist pattern 13is removed. Thus, as shown in FIGS. 15C and 15F, the portioncorresponding to the phase shifter formation region in the upper phaseshift film 12 is removed.

Next, as shown in FIG. 15D, a second resist pattern 14 that covers thesemi-light-shielding portion formation region and the phase shifterformation region is formed on the transparent substrate 10. That is tosay, a second resist pattern 14 that has a removed portion in theopening formation region is formed on the transparent substrate 10.Thereafter, the upper phase shift film 12 and the lower phase shift film11 are etched sequentially with the second resist pattern 14 as a maskto pattern each phase shift film. Then, the second resist pattern 14 isremoved. Thus, as shown in FIGS. 15E and 15G, the portions correspondingto the opening formation region in the lower phase shift film 11 and theupper phase shift film 12 are removed, and thus the photomask of thesecond variation of the first embodiment is completed.

According to the second variation of the first embodiment, the followingadvantages can be obtained, in addition to those of the firstembodiment. In this variation, the process of removing the portioncorresponding to the phase shifter formation region in the upper phaseshift film 12 (see FIG. 15C) and the process of removing the portioncorresponding to the opening formation region in the upper phase shiftfilm 12 (see FIG. 15E) are performed separately. Therefore, if theopening is apart from the phase shifter with a small distance, in otherwords, if a semi-light-shielding portion having a small width made of amultilayered structure of the lower phase shift film 11 and the upperphase shift film 12 is present between the opening and the phaseshifter, the margin for photomask process is increased.

In the second variation of the first embodiment, before performing theprocess of removing the portion corresponding to the phase shifterformation region in the upper phase shift film 12, the process ofremoving the portions corresponding to the opening formation region inthe lower phase shift film 11 and the upper phase shift film 12 may beperformed.

Second Embodiment

Hereinafter, a photomask according to a second embodiment of the presentinvention, a method for producing the photomask and a method for forminga pattern using the photomask will be described with reference to theaccompanying drawings. The photomask of the second embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

FIG. 16A shows an example of a desired pattern to be formed with thephotomask of the second embodiment. In this embodiment as well as thefirst embodiment, the description is based on the assumption that thepositive resist process is used. Furthermore, in this embodiment, thetransmittance is expressed by an effective transmittance when thetransmittance of the transparent substrate is taken as 100%, unlessotherwise specified.

FIG. 16B is a plan view of the photomask of the second embodiment, morespecifically, a photomask for forming the desired pattern shown in FIG.16A. As shown in FIG. 16B, openings (light-transmitting portions) areprovided so as to correspond to resist-removed portions in the desiredpattern. Furthermore, a semi-light-shielding portion having a lowtransmittance (about 6 to 15%) that does not allow the resist film to beexposed and transmits exposure light in the same phase as that of theopening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lighttransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

In the second embodiment, the phase shifters are arranged in such amanner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

FIG. 16C is a cross-sectional view taken along line AA′ in FIG. 16B,that is a cross-sectional view of the photomask-of the secondembodiment. As shown in FIG. 16C, the surface of the transparentsubstrate 20 in the opening (light-transmitting portion) formationregion is exposed. A lower phase adjusting film 21 is formed on thetransparent substrate 20 in the phase shifter (peripheral portion)formation region. The lower phase adjusting film 21, a transmittanceadjusting film 22 and an upper phase adjusting film 23 are formedsequentially on the transparent substrate 20 in the semi-light-shieldingportion formation region. The lower phase adjusting film 21 and theupper phase adjusting film 23 constitute a phase shift film thattransmits exposure light with a phase difference (opposite phase) of 180degrees (more specifically (150+360×n) degrees or more and (210+360×n)degrees or less (where n is an integer)) between this film and theopening. The transmittance adjusting film 22 has a lower transmittancethan those of the lower phase adjusting film 21 and the upper phaseadjusting film 23. As the lower phase shift film 21 and the upper phaseadjusting film 23, an oxide film such as SiO₂ film can be used. As thetransmittance adjusting film 22, a thin film (having a thickness of 30nm or less) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo—Si alloy or a Ti—Si alloy can be used.The lower phase adjusting film 21 is a phase shift film that has a veryhigh transmittance as a single film and transmits exposure light in aphase opposite to that of the opening (transparent substrate 20). Thetransmittance of the transmittance adjusting film 22 is set such thatthe multilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23has a predetermined transmittance low transmittance that does not allowthe resist film to be exposed) with respect to exposure light. Moreover,the multilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23transmits exposure light in the same phase (more specifically, the phasedifference of (−30+360×n) degrees or more and (30+360×n) degrees orless, (where n=an integer)) between this structure and the opening(transparent substrate 20). That is to say, the multilayered structureof the lower phase adjusting film 21, the transmittance adjusting film22 and the upper phase adjusting film 23 constitute asemi-light-shielding portion that transmits exposure light in the samephase as that of the opening and has a predetermined transmittance withrespect to exposure light. Thus, the peripheral portion, that is, aphase shifter, having a single layered structure of the lower phaseadjusting film 21 is formed between the semi-light-shielding portion andthe opening, and thus an outline enhancement mask is realized. However,in order to enhance the contrast by the outline enhancement method, itis necessary to limit the width of the phase shifter to a predeterminedsize.

A method for producing the photomask of the second embodiment is asfollows. The lower phase adjusting film 21, the transmittance adjustingfilm 22 and the upper phase adjusting film 23 are formed sequentially onthe transparent substrate 20 made of a material havinglight-transmitting properties with respect to exposure light (e.g.,quartz). Thereafter, the upper phase adjusting film 23, thetransmittance adjusting film 22 and the lower phase adjusting film 21are selectively etched sequentially. More specifically, if the lowerphase adjusting film 21 is regarded as a lower phase shift film and thetransmittance adjusting film 22 and the upper phase adjusting film 23are regarded as an upper phase shift film, the method for producing thephotomask of the first embodiment shown in FIGS. 13 to 15 can be used asit is to produce the photomask of the second embodiment.

Next, a method for forming a pattern using the photomask of the secondembodiment will be described. In this case, as described with referenceto the principle of the outline enhancement method when transferring amask pattern in a reduced size with an exposure apparatus, it ispreferable to use an oblique incident exposure light source as shown inFIGS. 11B to 11D in order to form an image having a high contrast withthe outline enhancement mask.

FIGS. 17A to 17D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the second embodiment.

First, as shown in FIG. 17A, after a film 201 to be processed such as ametal film or an insulating film is formed on a substrate 200, as shownin FIG. 17B, a positive resist film 202 is formed on the film 201 to beprocessed.

Next, as shown in FIG. 17C, the photomask of the second embodimentincluding the semi-light-shielding portion made of the multilayeredstructure of the lower phase adjusting film 21, the transmittanceadjusting film 22 and the upper phase adjusting film 23, and a phaseshifter made of the single layered structure of the lower phaseadjusting film 21 is irradiated with exposure light 203 with an obliqueincident exposure light source to expose the resist film 202 withtransmitted light 204 transmitted through the photomask. In this case,the semi-light-shielding portion having a low transmittance is used asthe mask pattern, so that the entire resist film 202 is exposed withweak energy. However, as shown in FIG. 17C, only a latent image portion202 a of the resist film 202 corresponding to the light-transmittingportion (opening) in the photomask is irradiated with exposure energythat is sufficient to dissolve the resist film 202 in a developingprocess.

Next, the latent image portion 202 a is removed by performingdevelopment with respect to the resist film 202, so that as shown inFIG. 17D, a resist pattern 205 is formed. In this case, in the exposureprocess shown in FIG. 17C, light in the periphery of the opening iscanceled, so that a portion corresponding to the phase shifter(peripheral portion) in the resist film 202 is substantially notirradiated with exposure energy. Therefore, the contrast in the lightintensity distribution between the light transmitted through the openingand the light transmitted through the peripheral portion, in otherwords, the contrast in the light intensity distribution between thelight with which the latent image portion 202 a is irradiated and thelight with which the periphery of the latent portion 202 a is irradiatedcan be enhanced. Therefore, the energy distribution in the latentportion 202 a is changed sharply, so that a resist pattern 205 having asharp shape can be formed.

As described above, according to the second embodiment, the phaseshifter (peripheral portion) made of a single layered structure of thelower phase adjusting film 21 is sandwiched by the opening(light-transmitting portion) made of the exposed portion of thetransparent substrate 20 and the semi-light-shielding portion made of amultilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23.In this case, the multilayered structure of the lower phase adjustingfilm 21, the transmittance adjusting film 22 and the upper phaseadjusting film 23 transmit exposure light in the same phase as that ofthe opening, whereas the single layered structure of the lower phaseadjusting film 21 transmits exposure light in a phase opposite to thatof the opening. Therefore, the contrast in the light intensitydistribution between the opening and the phase shifter can be enhancedby mutual interference between the light transmitted through the openingand the light transmitted through the phase shifter. This contrastenhancement effect also can be obtained when a fine isolatedresist-removed portion (i.e., a fine isolated space patterncorresponding to the light-transmitting portion) is formed with obliqueincident exposure (off-axis illumination), for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

According to the second embodiment, the lower phase adjusting film 21,the transmittance adjusting film 22, the upper phase adjusting film 23that are laminated on the transparent substrate 20 are etchedselectively, so that a mask pattern with any shape that has thesemi-light-shielding portion and the phase shifter (peripheral portion)can be easily produced.

According to the second embodiment, a phase shifter with any shape canbe formed by processing the transmittance adjusting film 22 and theupper phase adjusting film 23 of the multilayered structure of the lowerphase adjusting film 21, the transmittance adjusting film 22 and theupper phase adjusting film 23 constituting the semi-light-shieldingportion. Therefore, as the layout of the outline enhancement mask, notonly the type shown in FIGS. 16B and 16C, that is, the type shown inFIG. 8B, but also all the types shown in FIGS. 8A to 8F, for example,can be realized.

According to the second embodiment, the semi-light-shielding portion isformed by providing the transmittance adjusting film 22 having a lowertransmittance than that of the phase adjusting films between the lowerphase adjusting film 21 and the upper phase adjusting film 23.Therefore, the difference in the transmittance between thesemi-light-shielding portion and the phase shifter (peripheral portion)made of the single layered structure of the lower phase adjusting film21 can be increased, so that the contrast in the light intensitydistribution between the opening (light-transmitting portion) and theperipheral portion can be enhanced more significantly.

In the second embodiment, it is preferable that the transmittance of thesemi-light-shielding portion of the photomask is 6% or more and 15% orless. Thus, the contrast enhancement effect can be obtained reliablywhile preventing a reduction in thickness of the resist film in patternformation.

In the second embodiment, the description is based on the use of thepositive resist process, but the negative resist process can be used,instead of the positive resist process. In this case, in either one ofthe processes, as the exposure light source, the i line (wavelength 365nm), KrF excimer laser-light (wavelength 248 nm), ArF excimer laserlight (wavelength 193 nm), or F₂ excimer laser light (wavelength 157 nm)can be used, for example.

In the second embodiment, for example, as shown in FIG. 16C, themultilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23 isused as the semi-light-shielding portion. However, instead of this, forexample, as shown in FIG. 18A, even if a two layered structure of thephase adjusting film 21 as the lower layer and the transmittanceadjusting film 22 as the upper layer is used, the photomask having thesame effect can be realized. More specifically, in the structure shownin FIG. 18A, the phase adjusting film 21 and the transmittance adjustingfilm 22 formed only on the phase adjusting film 21 in thesemi-light-shielding portion formation region constitute thesemi-light-shielding film that transmits exposure light in the samephase as that of the opening. The transmittance adjusting film 22 has arelatively low transmittance with respect to exposure light, whereas thephase adjusting film 21 has a relatively high transmittance. Thus, thesemi-light-shielding film made of the phase adjusting film 21 and thetransmittance adjusting film 22 has a transmittance that allows exposurelight to be transmitted partially. The transmittance adjusting film 22transmits exposure light in the same phase as that of the opening, andthe portion of the phase adjusting film 21 in the semi-light-shieldingportion formation region transmits exposure light in the same phase asthat of the opening. On the other hand, the portion of the phaseadjusting film 21 in the phase shifter (peripheral portion) formationregion is made thin so as to have a thickness that allows exposure lightto be transmitted in the phase opposite to that of the opening. Whencomparing the structure shown in FIG. 16C and the structure shown inFIG. 18A, the structure shown in FIG. 16C is better than the structureshown in FIG. 18A in that the transmittance adjusting film 22 can beutilized as an etching stopper when etching the upper phase adjustingfilm 23 in mask processing. On the other hand, the structure shown inFIG. 18A is better than the structure shown in FIG. 16C in that thephase shifter can be formed by changing the thickness of the phaseadjusting film 21 formed as a single film by etching, in other words, inthat the photomask structure is simple. Furthermore, according to thestructure shown in FIG. 18A, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for thesemi-light-shielding film made of the phase adjusting film 21 and thetransmittance adjusting film 22. Moreover, a combination of the materialof the transmittance adjusting film 22 and the material of the phaseadjusting film 21 makes it possible to improve the selection ratio atetching for processing the semi-light-shielding film.

In the second embodiment, for example, as shown in FIG. 16C, thetransmittance adjusting film 22 is not formed on the lower phaseadjusting film 21 in the phase shifter formation region. However,instead of this, as shown in FIG. 18B, the transmittance adjusting film22 may be formed on the lower phase adjusting film 21 in the phaseshifter formation region. In other words, the phase shifter made of asingle layered structure of the lower phase adjusting film 21 can bereplaced by a phase shifter made of a multilayered structure of thelower phase adjusting film 21 and the transmittance adjusting film 22.In this case, the transmittance of the phase shifter and thetransmittance of the semi-light-shielding portion are in the same level.When comparing the structure shown in FIG. 16C and the structure shownin FIG. 18B, the structure shown in FIG. 16C is better than thestructure shown in FIG. 18B in that the transmittance of thesemi-light-shielding portion is higher than that of the phase shifter,that is, in that the contrast enhancement effect by the outlineenhancement method is improved On the other hand, the structure shown inFIG. 18B is better than the structure shown in FIG. 16C in that the sizeof the phase shifter can be increased to the extent corresponding to howlow the transmittance of the phase shifter is, that is, in that the maskprocessing is easy.

Furthermore, a photomask having the same effect can be realized, even ifa two layered structure of the transmittance adjusting film 22 as thelower layer and the phase adjusting film 23 as the upper layer is usedas the semi-light-shielding portion and the phase shifter, for example,as shown in FIG. 18C, instead of the structure shown in FIG. 18B. Morespecifically, in the structure shown in FIG. 18C, the transmittanceadjusting film 22 and the phase adjusting film 23 in thesemi-light-shielding portion formation region constitute asemi-light-shielding film that transmits exposure light in the samephase as that of the opening. Furthermore, the transmittance adjustingfilm 22 has a relatively low transmittance with respect to exposurelight, whereas the phase adjusting film 23 has a relatively hightransmittance with respect to exposure light. Thus, thesemi-light-shielding film made of the transmittance adjusting film 22and the phase adjusting film 23 has a transmittance that allows exposurelight to be transmitted partially. The transmittance adjusting film 22transmits exposure light in the same phase as that of the opening, andthe portion of the phase adjusting film 23 in the semi-light-shieldingportion formation region transmits exposure light in the same phase asthat of the opening. On the other hand, the portion of the phaseadjusting film 23 in the phase shifter (peripheral portion) formationregion is made thin so as to have a thickness that allows exposure lightto be transmitted in the phase opposite to that of the opening. Whencomparing the structure shown in FIG. 18B and the structure shown inFIG. 18C, the structure shown in FIG. 18C is better in that thephotomask structure is simple. In addition, in the case where the phaseadjusting film 23 is formed of a material that hardly can increase theetching selection ratio with respect to the transparent substrate 20made of quartz or the like, the structure shown in FIG. 18C is better inthat the transmittance adjusting film 22 can be utilized as an etchingstopper for preventing etching of quartz when etching the phaseadjusting film 23. Furthermore, according to the structure shown in FIG.18C, a combination of a desired phase difference and a desiredtransmittance can be selected arbitrarily for the semi-light-shieldingfilm made of the phase adjusting film 23 and the transmittance adjustingfilm 22. Moreover, a combination of the material of the transmittanceadjusting film 22 and the material of the phase adjusting film 23 makesit possible to improve the selection ratio at etching for processing thesemi-light-shielding film.

In the second embodiment, as seen from the comparison of the structureshown in FIG. 16C and the structure shown in FIG. 18B, phase shiftershaving different transmittances can be formed with the same multilayeredstructure in which the transmittance adjusting film 22 is presentbetween the lower phase adjusting film 21 and the upper phase adjustingfilm 23 by changing the processing method of the transmittance adjustingfilm 22. In other words, when the structure in which the transmittanceadjusting film is sandwiched by the two phase adjusting films is used,both the structure shown in FIG. 16C and the structure shown in FIG. 18Bcan be realized in the same photomask, so that the transmittance of thephase shifter (peripheral portion) can be changed depending on thepattern shape. Furthermore, for example, as shown in FIG. 18D, when thestructure in which the transmittance adjusting film 22 is formedpartially on the lower phase adjusting film 21 in the phase shifterformation region is used, the effective transmittance of the phaseshifter can be adjusted finely by the area ratio of the phase shifterthat is covered with the transmittance adjusting film 22 (=(the area ofthe transmittance adjusting film 22 in the phase shifter formationregion)/(the area of the phase shifter)). Therefore, it is possible toarbitrarily change the transmittance of the phase shifter depending onthe pattern shape on the same photomask.

Third Embodiment

Hereinafter, a photomask according to a third embodiment of the presentinvention, a method for producing the photomask and a method for forminga pattern using the photomask will be described with reference to theaccompanying drawings. The photomask of the third embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

FIG. 19A shows an example of a desired pattern to be formed with thephotomask of the third embodiment. In this embodiment as well as thefirst embodiment, the description is based on the assumption that thepositive resist process is used. In this embodiment the transmittance isexpressed by an effective transmittance when the transmittance of thetransparent substrate is taken as 100%, unless otherwise specified.

FIG. 19B is a plan view of the photomask of the third embodiment, morespecifically, a photomask for forming the desired pattern shown in FIG.19A. As shown in FIG. 19B, openings light-transmitting portions) areprovided so as to correspond to resist-removed portions in the desiredpattern. Furthermore, a semi-light-shielding portion that has a lowtransmittance (about 6 to 15%) that does not allow the resist film to beexposed and transmits exposure light in the same phase as that of theopening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lightstransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

In the third embodiment, the phase shifters are arranged in such amanner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

FIG. 19C is a cross-sectional view taken along line AA′ in FIG. 19B,that is a cross-sectional view of the photomask of the third embodiment.As shown in FIG. 19C, the surface of the transparent substrate 30 in theopening formation region is exposed. A semi-light-shielding film(half-tone film) 31 having a low transmittance (about 6 to 15%) thatdoes not allow the resist film to be exposed is formed on thetransparent substrate 30 in the semi-light-shielding portion formationregion and the phase shifter formation region. As the portion of thehalf-tone film 31, an oxide film such as ZrSiO, CrAlO, TaSiO, MoSiO orTiSiO can be used. The portion of the half-tone film 31 in thesemi-light-shielding portion formation region has a thickness thatcauses a phase difference (the same phase) of 360 degrees (morespecifically, (−30+360×n) degrees or more and (30+360×n) degrees or less(where n=an integer)) with respect to exposure light between this filmand the transparent substrate 30 (opening). On the other hand, theportion of the half-tone film 31 in the phase shifter formation regionhas a small thickness that causes a phase difference (opposite phase) of(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer) between this film and the opening. That is to say, thehalf-tone film 31 can transmit exposure light in a phase opposite tothat of the opening when its thickness is changed.

As described above, in the photomask of this embodiment, the peripheralportion, that is, the phase shifter, made of a thin portion of thehalf-tone film 31 is formed between the semi-light-shielding portionmade of a thick portion of the half-tone film 31 and the opening(light-transmitting portion), and thus the function of the outlineenhancement mask is realized. However, in this phase shifter, bydecreasing the thickness of the half-tone phase film 31, phase inversionoccurs and the transmittance with respect to exposure light is madelarger than that of the semi-light-shielding portion made of the thickportion of the half-tone film 31. Furthermore, it is necessary to limitthe width of the phase shifter to a predetermined size or less in orderto enhance the contrast by the outline enhancement method.

A method for producing the photomask of the third embodiment is asfollows. The half-tone film 31 is formed on the transparent substrate 30made of a material having light-transmitting properties with respect toexposure light (e.g., quartz). Thereafter, the half-tone film 31 isselectively etched.

Next, a method for forming a pattern using the photomask of the thirdembodiment will be described. In this case, as described with referenceto the principle of the outline enhancement method when transferring amask pattern in a reduced size with an exposure apparatus, it ispreferable to use an oblique incident exposure light source as shown inFIGS. 11B to 11D in order to form an image having a high contrast withthe outline enhancement mask.

FIGS. 20A to 20D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the third embodiment.

First, as shown in FIG. 20A, after a film 301 to be processed such as ametal-film or an insulating film is formed on a substrate 300, as shownin FIG. 20B, a positive resist film 302 is formed on the film 301 to beprocessed.

Next, as shown in FIG. 20C, the photo mask of the third embodimentincluding the semi-light-shielding portion made of the thick portion ofthe half-tone film 31 and the phase shifter made of the thin portion ofthe half-tone film 31 is irradiated with exposure light 303 with anoblique incident exposure light source to expose the resist film 302with transmitted light 304 transmitted through the photomask. In thiscase, as the mask pattern, the semi-light-shielding portion having a lowtransmittance is used, so that the entire resist film 302 is exposedwith weak energy. However, as shown in FIG. 20C, only a latent imageportion 302 a of the resist film 302 corresponding to thelight-transmitting portion (opening) in the photomask is irradiated withexposure energy that is sufficient to dissolve the resist film 302 in adeveloping process.

Next, the latent image portion 302 a is removed by performingdevelopment with respect to the resist film 302, so that as shown inFIG. 20D, a resist pattern 305 is formed. In this case, in the exposureprocess shown in FIG. 20C, light around the opening is canceled, so thata portion corresponding to the phase shifter (peripheral portion) in theresist film 302 is substantially not irradiated with exposure energy.Therefore, the contrast in the light intensity distribution between thelight transmitted through the opening and the light transmitted throughthe peripheral portion, in other words, the contrast in the lightintensity distribution between the light with which the latent imageportion 302 a is irradiated and the light with which the periphery ofthe latent portion 302 a is irradiated can be enhanced. Therefore, theenergy distribution in the latent portion 302 a is changed sharply, sothat a resist pattern 305 having a sharp shape can be formed.

As described above, according to the third embodiment, the phase shifter(peripheral portion) made of the thin portion of the half-tone film 31is sandwiched by the opening (light-transmitting portion) made of theexposed portion of the transparent substrate 30 and thesemi-light-shielding portion made of the thick portion of the half-tonefilm 31. In this case, the thick portion of the half-tone film 31transmits exposure light in the same phase as that of the opening,whereas the thin portion of the half-tone film 31 transmits exposurelight in a phase opposite to that of the opening. Therefore, thecontrast in the light intensity distribution between the opening and thephase shifter can be enhanced by mutual interference between the lighttransmitted through the opening and the light transmitted through thephase shifter. This contrast enhancement effect also can be obtainedwhen a fine isolated resist-removed portion (i.e., a fine isolated spacepattern corresponding to the light-transmitting portion) is formed withoblique incident exposure, for example, in the positive resist process.That is to say, it is possible to miniaturize isolated space patternsand isolated line patterns or dense patterns at the same time withoblique incident exposure.

According to the third embodiment, the semi-light-shielding portion isconstituted by a single layered structure of the half-tone film 31, sothat the mask structure is very simple. Moreover, a phase shifter(peripheral portion) can be formed easily simply by partially reducingthe thickness of the half-tone film 31, in other words, by providing arecess in the half-tone film 31.

According to the third embodiment, the half-tone film 31 formed on thetransparent substrate 30 is etched selectively, so that a mask patternwith any shape that has the semi-light-shielding portion and the phaseshifter can be easily produced.

According to the third embodiment, a phase shifter with any shape can beformed by processing the half-tone film 31 serving as thesemi-light-shielding portion. Therefore, as the layout of the outlineenhancement mask, not only the type shown in FIGS. 19B and 19C, that is,the type shown in FIG. 8B, but also all the types shown in FIGS. 8A to8F, for example, can be realized.

In the third embodiment, it is preferable that the transmittance of thesemi-light-shielding portion of the photomask is 6% or more and 15% orless. Thus, the contrast enhancement effect can be obtained reliablywhile preventing a reduction in thickness of the resist film in patternformation.

In the third embodiment, the description is based on the use of thepositive resist process, but the negative resist process can be used,instead of the positive resist process. In this case, in either one ofthe processes, as the exposure light source, the i line (wavelength 365nm), KrF excimer laser light (wavelength 248 nm), ArF excimer laserlight (wavelength 193 nm), or F₂ excimer laser light (wavelength 157 nm)can be used, for example.

In the third embodiment, for example, a two layered structure in whichthe transmittance adjusting film having a low transmittance and thephase adjusting film having a high transmittance are laminated can beused as the structure of the half-tone film 31 (see FIGS. 18A and 18C).By doing this, a combination of a desired phase difference and a desiredtransmittance can be selected arbitrarily for the half-tone film 31.Moreover, the selection ratio at etching for processing the half-tonefilm 31 can be improved by a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm.

In the third embodiment, as shown in the plan view of FIG. 21A and thecorresponding cross-sectional view of FIG. 21B, the phase shifter(peripheral portion) made of the thin portion of the half-tone film 31is in contact with the opening (light-transmitting portion). However,instead of this, for example, as shown in the plan view of FIG. 21C andthe corresponding cross-sectional view of FIG. 21D, the thin portion ofthe half-tone film 31 can be spaced apart from the opening by apredetermined size. In other words, the phase shifter and the openingare spaced apart from each other, and a semi-light-shielding portionmade of the thick portion of the half-tone film 31 can be formed betweenthe phase shifter and the opening. In this case, as shown in FIG. 21Cand 21D, a phase shifter can be formed simply by partially reducing thethickness of the half-tone film 31, in other words, by providing arecess in the half-tone film 31. As a result, also in the case where asemi-light-shielding portion having a small width is present between thephase shifter and the opening, peeling of the film constituting thesemi-light-shielding portion having a small width can be suppressedbetter, compared with the case where a semi-light-shielding portion of amultilayered film structure is used. On the other hand, when thesemi-light-shielding portion with a small width having a multilayeredstructure is provided between the phase shifter and the opening, thesemi-light-shielding portion is present as a small isolated region ofthe upper film formed on the lower film, so that the isolated regiontends to be peeled while processing the upper film.

Fourth Embodiment

Hereinafter, a photomask according to a fourth embodiment of the presentinvention, a method for producing the photomask and a method for forminga pattern using the photomask will be described with reference to theaccompanying drawings. The photomask of the fourth embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

FIG. 22A shows an example of a desired pattern to be formed with thephotomask of the fourth embodiment. In this embodiment as well as thefirst embodiment, the description is based on the assumption that thepositive resist process is used. In this embodiment, the transmittanceis expressed by an effective transmittance when the transmittance of thetransparent substrate is taken as 100%, unless otherwise specified.

FIG. 22B is a plan view of the photomask of the fourth embodiment, morespecifically, a photomask for forming the desired pattern shown in FIG.22A. As shown in FIG. 22B, openings (light-transmitting portions) areprovided so as to correspond to resist-removed portions in the desiredpattern. Furthermore, a semi-light-shielding portion that has a lowtransmittance (about 6 to 15%) that does not allow the resist film to beexposed and transmits exposure light in the same phase as that of theopening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lightstransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

In the fourth embodiment, the phase shifters are arranged in such amanner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

FIG. 22C is a cross-sectional view taken along line AA′ in FIG. 22B,that is a cross-sectional view of the photomask of the fourthembodiment. As shown in FIG. 22C, the surface of the transparentsubstrate 40 in the opening formation region is exposed. Asemi-light-shielding film (half-tone film) 41 having a low transmittance(about 6 to 15%) that does not allow the resist film to be exposed isformed on the transparent substrate 40 in the semi-light-shieldingportion formation region. The half-tone film 41 generates a phasedifference (the same phase) of 360 degrees with respect to exposurelight (more specifically, (−30+360×n) degrees or more and (30+360×n)degrees or less, (where n=an integer)) between this film and thetransparent substrate 40 (opening). The portion of the transparentsubstrate 40-in the phase shifter formation region is dug down so as tohave a thickness that causes a phase difference (opposite phase) of(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer) between this film and the opening. That is to say, the dugportion 40 a is provided in the transparent substrate 40 in the phaseshifter formation region.

As the half-tone film 41, a thin film (having a thickness of 30 nm orless) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo-Si alloy or a Ti—Si alloy can be used.In this embodiment, as the half-tone film 41, for example, a singlelayered structure of a light-shielding film (e.g., a chromium film usedas a light-shielding film of a regular photomask) that is made thin soas to have a very small phase difference between this film and theopening and thus has a low transmittance that does not allow the resistfilm to be exposed is used.

As described above, according to the photomask of this embodiment, thephase shifter made of the dug portion 40 a of the transparent substrate40 is formed between the semi-light-shielding portion made of thehalf-tone film 41 and the opening (light-transmitting portion), and thusthe function of the outline enhancement mask is realized. However, it isnecessary to limit the width of the phase shifter to a predeterminedsize or less in order to enhance the contrast by the outline enhancementmethod.

Next, a method for forming a pattern using the photomask of the fourthembodiment will be described. In this case, as described with referenceto the principle of the outline enhancement method when transferring amask pattern in a reduced size with an exposure apparatus, it ispreferable to use an oblique incident exposure light source as shown inFIGS. 11B to 11D in order to form an image having a high contrast withthe outline enhancement mask.

FIGS. 23A to 23D are cross-sectional views showing the processes of amethod forming a pattern with the photomask of the fourth embodiment.

First, as shown in FIG. 23A, after a film 401 to be processed such as ametal film or an insulating film is formed on a substrate 400, as shownin FIG. 23B, a positive resist film 402 is formed on the film 401 to beprocessed.

Next, as shown in FIG. 23C, the photomask of the fourth embodimentincluding the semi-light-shielding portion made of the half-tone film 41and the phase shifter (peripheral portion) made of the dug portion 40 aof the transparent substrate 40 is irradiated with exposure light 403with an oblique incident exposure light source to expose the resist film402 with transmitted light 404 transmitted through the photomask. Inthis case, as the mask pattern, the semi-light-shielding portion havinga low transmittance is used, so that the entire resist film 402 isexposed with weak energy. However, as shown in FIG. 23C, only a latentimage portion 402a of the resist film 402 corresponding to thelight-transmitting portion (opening) in the photomask is irradiated withexposure energy that is sufficient to dissolve the resist film 402 in adeveloping process.

Next, the latent image portion 402 a is removed by performingdevelopment with respect to the resist film 402, so that as shown inFIG. 23D, a resist pattern 405 is formed. In this case, in the exposureprocess shown in FIG. 23C, light around the opening is canceled, so thata portion corresponding to the phase shifter (peripheral portion) in theresist film 402 is substantially not irradiated with exposure energy.Therefore, the contrast in the light intensity distribution between thelight transmitted through the opening and the light transmitted throughthe peripheral portion, in other words, the contrast in the lightintensity distribution between the light with which the latent imageportion 402 a is irradiated and the light with which the periphery ofthe latent portion 402 a is irradiated can be enhanced. Therefore, theenergy distribution in the latent portion 402 a is changed sharply, sothat a resist pattern 405 having a sharp shape can be formed.

Next, a method for producing a photomask of the fourth embodiment willbe described with reference to the drawings.

FIGS. 24A to 24E are cross-sectional views showing the processes of amethod for producing the photomask of the fourth embodiment. FIG. 24F isa plan view corresponding to the cross-sectional view of FIG. 24C. FIG.24G is a plan view corresponding to the cross-sectional view of FIG.24E.

First, as shown in FIG. 24A, the half-tone film 41 is formed on thetransparent substrate 40 made of a material having light-transmittingproperties with respect to exposure light such as quartz. As thehalf-tone film 41, a single layered light-shielding film with a reducedthickness is used.

Next, as shown in FIG. 24B, a first resist pattern 42 that covers thesemi-light-shielding portion formation region and the opening(light-transmitting portion) formation region is formed on thetransparent substrate 40. That is, a first resist pattern 42 having aremoved portion in the phase shifter (peripheral portion) formationregion is formed on the transparent substrate 40. Thereafter, thehalf-tone film 41 and the transparent substrate 40 are etched with thefirst resist pattern 42 as a mask, and then the first resist pattern 42is removed. Thus, as shown in FIGS. 24C and 24F, the portionscorresponding to the phase shifter formation region in the half-tonefilm 41 are removed. The transparent substrate 40 in the phase shifterformation region is dug down so as to have a thickness that transmitsexposure light in a phase opposite to that of the opening. Morespecifically, a dug portion 40 a that causes phase inversion of 180degrees (more specifically, a phase difference of (150 +360×n) degreesor more and (210+360×n) degrees or less, where n=an integer) in theportion corresponding to the phase shifter formation region in thetransparent substrate 40.

Next, as shown in FIG. 24D, a second resist pattern 43 that covers theportion corresponding to the semi-light-shielding portion formationregion in the half-tone film 41 is formed on the transparent substrate40. Thereafter, the half-tone film 41 is etched with the second resistpattern 43 as a mask, and then the second resist pattern 43 is removed.Thus, as shown in FIGS. 24E and 24G, the portion corresponding to theopening formation region in the half-tone film 41 is removed, and thusthe photomask of the fourth embodiment is completed. That is to say, thephotomask of the fourth embodiment having the plane structure of theoutline enhancement mask can be easily formed by, as a mask blank,preparing a transparent substrate in which a light-shielding film with areduced thickness is deposited, and then performing etching with respectto the light-shielding film and the transparent substrate sequentially.

As described above, according to the fourth embodiment, the phaseshifter (peripheral portion) made of the dug portion 40 a in thetransparent substrate 40 is sandwiched by the opening(light-transmitting portion) made of the exposed portion of thetransparent substrate 40 and the semi-light-shielding portion made ofthe half-tone film 41. The half-tone film 41 transmits exposure light inthe same phase as that of the opening, whereas the dug portion 40 atransmits exposure light in a phase opposite to that of the opening.Therefore, the contrast in the light intensity distribution between theopening and the phase shifter can be enhanced by mutual interferencebetween the light transmitted through the opening and the lighttransmitted through the phase shifter. This contrast enhancement effectalso can be obtained when a fine isolated resist-removed portion (i.e.,a fine isolated space pattern corresponding to the light-transmittingportion) is formed with oblique, incident exposure, for example, in thepositive resist process. That is to say, it is possible to miniaturizeisolated space patterns and isolated line patterns or dense patterns atthe same time with oblique incident exposure.

According to the fourth embodiment, the semi-light-shielding portion isconstituted by a single layered structure of the half-tone film 41, sothat the mask structure is simple.

According to the fourth embodiment, after the half-tone film 41 isformed on the transparent substrate 40, the half-tone film 41 and thetransparent substrate 40 are etched selectively, so that a mask patternwith any shape that has the semi-light-shielding portion and the phaseshifter (peripheral portion) can be easily realized.

According to the fourth embodiment, a phase shifter with any shape canbe formed by processing the multilayered structure of the transparentsubstrate 40 and the half-tone film 41 by the method for producing aphotomask shown in, for example, FIGS. 24A to 24E. Therefore, as thepattern layout of the outline enhancement mask, not only the type shownin FIGS. 22B and 22C, that is, the type shown in FIG. 8B, but also allthe types shown in FIGS. 8A to 8F, for example, can be realized.

According to the fourth embodiment, as the half-tone film 41, a filmobtained by reducing the thickness of a light-shielding film for aregular photomask is used, so that a substrate to be prepared as a maskblank can be simplified. That is to say, photomask process can beperformed easily only by preparing a transparent substrate in which asingle layered thin film is formed as a mask blank, and etching each ofthe single layered thin film and the transparent substrate. For example,the transparent substrate in which a two layered structure of a phaseadjusting film and a transmittance adjusting film is formed is used as amask blank for a regular half-tone phase-shifting mask. However, in thisembodiment, a half-tone phase-shifting mask in which the phase adjustingfilm is not formed, in other words, a mask blank in which only thetransmittance adjusting film is formed on the transparent substrate canbe used. That is to say, a conventional technology can be utilized inproduction of a mask blank by using a light-shielding film with areduced thickness as the half-tone film 41, which-is advantageous inpractice.

Hereinafter, the results of examination with simulations of an influenceof a phase change (a phase difference caused between the opening and thesemi-light-shielding portion) due to the use of the light-shielding filmwith a reduced thickness as the half-tone phase film 41, that is, thesemi-light-shielding portion on the pattern formation will be describedwith reference to FIGS. 25A to 25C. The simulation conditions are suchthat the wavelength λ of the exposure light is 0.193 μm (ArF lightsource), the numerical aperture NA of the projection optical system ofthe exposure apparatus is 0.6, and annular illumination is used.

FIG. 25A shows a plan view of an outline enhancement mask used in thesimulations. As shown in FIG. 25A, the width of the opening and thephase shifter is 200 nm and 50 nm, respectively. The transmittance ofthe opening, the phase shifter and the semi-light-shielding portion is100%, 100% and 7.5%, respectively. The phase shifter generates a phasedifference of 180 degrees between this portion and the opening, and thesemi-light-shielding portion generates a phase difference of 0 to 30degrees between this portion and the opening.

FIG. 25B shows the simulation results of the light intensitydistribution corresponding to line AA′ when exposure is performed withrespect to the outline enhancement mask shown in FIG. 25A in such amanner that a phase difference of 0 degrees, 10 degrees, 20 degrees or30 degrees is generated between the semi-light-shielding portion and theopening. As shown in FIG. 25B, if the phase difference between thesemi-light-shielding portion and the opening is not more than 30 degreeor so, the contrast in the light intensity distribution is notsubstantially affected.

FIG. 25C shows the simulation results of the focus dependence of thesize (CD: Critical Dimension) of the finished pattern when exposure isperformed with respect to the outline enhancement mask shown in FIG. 25Ain such a manner that a phase differences of 0 degrees, 10 degrees, 20degrees or 30 degrees is generated between the semi-light-shieldingportion and the opening. As shown in FIG. 25C, if the phase differencebetween the semi-light-shielding portion and the opening is changed, thebest focus position in which the CD is the peak is changed. However,even if the phase difference is changed, the unlikelihood of CD changewith respect to the focus variation, that is, the depth of focus issubstantially not changed. No problem is caused in pattern formation,even if the best focus positions are varied in the same manner, at allportions on the photomask. Only the depth of focus is an issue inpattern formation. That is to say, if the phase difference between thesemi-light-shielding portion and the opening is up to about 30 degrees,there is no problem in terms of the focus characteristics.

Therefore, in this embodiment, when a light-shielding film with areduced thickness is used as the half-tone film 41 serving as asemi-light-shielding portion, the outline enhancement mask in a strictsense (the phase difference between the semi-light-shielding portion andthe opening is 0 degree) cannot be realized, but if the phase differencethat is caused by the reduction of the film is about 30 degrees or less,the effect of the outline enhancement method is not lost. Morespecifically, when Ta, Cr or alloys containing Ta or Cr or the like isused as the material of the light-shielding film, the thickness of thelight-shielding film that generates a phase difference of about 30degrees between this film and the opening with respect to light from anArF light source is approximately 30 nm or more. This thickness issufficient to realize a transmittance of 10% or less.

In the fourth embodiment, it is preferable that the transmittance of thesemi-light-shielding portion is 6% or more and 15% or less. Thus, thecontrast enhancement effect can be obtained reliably while preventing areduction in thickness of the resist film in pattern formation.

In the fourth embodiment, the description is based on the use of thepositive resist process, but the negative resist process can be used,instead of the positive resist process. In this case, in either one ofthe processes, as the exposure light source, the i line (wavelength 365nm), KrF excimer laser light (wavelength 248 nm), ArF excimer laserlight (wavelength 193 run), or F₂ excimer laser light (wavelength 157nm) can be used, for example.

In the fourth embodiment, for example, a two layered structure in whichthe transmittance adjusting film having a low transmittance and thephase adjusting film having a high transmittance are laminated can beused as the structure of the half-tone film 41. By doing this, acombination of a desired phase difference (more specifically (−30+360×n)degrees or more and (30+360×n) degrees or less) and a desiredtransmittance can be selected arbitrarily for the half-tone film 41.Moreover, the selection ratio at etching for processing the half-tonefilm 41 can be improved by a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm. Furthermore, for example, it is possible to set a phase differencebetween the opening and the semi-light-shielding portion to 0 degree bydepositing a phase adjusting film on the single layered thinlight-shielding film used as the half-tone film 41 in this embodiment.

In the fourth embodiment, as shown in the plan view of FIG. 22B and thecorresponding cross-sectional view of FIG. 22C, the dug portion 40 a inthe transparent substrate 40, that is, the phase shifter is in contactwith the opening. However, instead of this, for example, as shown in theplan view of FIG. 26A and the corresponding cross-sectional view of FIG.26B, the half-tone film 41 is used as the semi-light-shielding portion,and the dug portion 40 a in the transparent substrate 40 can be spacedapart from the opening by a predetermined size. In other words, thephase shifter (peripheral portion) and the opening (light-transmittingportion) are spaced apart from each other, and a semi-light-shieldingportion can be formed between the phase shifter and the opening. FIG.26C shows a cross-sectional structure of a photomask using a semi-lightshielding portion in which the phase adjusting film is deposited on asingle layered thin film having a low transmittance, instead of thesemi-light-shielding portion constituted only by the half-tone film 41in the photomask shown in FIG. 26B. In the photomask shown in the planview of FIG. 26C, a two layered structure in which a transmittanceadjusting film 41A having a low transmittance and a phase adjusting film41B having a high transmittance are laminated is used as thesemi-light-shielding portion, and thus the phase difference between thesemi-light-shielding portion and the opening is set to 0 degree. As thetransmittance adjusting film 41A, a-thin film (having a thickness of 30nm or less) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo—Si alloy or a Ti—Si alloy can be used.As the phase adjusting film 41B, an oxide film such as SiO₂ film can beused.

As the photomask shown in FIG. 26C, when the semi-light-shieldingportion having a small width that spaces the phase shifter apart fromthe opening constitutes a thick multilayered film structure, morespecifically, a small isolated region of a thick phase adjusting film41B formed on the lower transmittance adjusting film 41A is presentbetween the phase shifter and the opening, the isolated region tends tobe peeled during the processing of the phase adjusting film 41B. Asopposed to this, the cross-sectional structure of the photomask can besuch as shown in FIG. 26D by utilizing the advantage that no problem iscaused if a phase difference of up to 30 degrees is generated betweenthe phase shifter and the opening. That is to say, a single layeredstructure of a thin transmittance adjusting film 41A that is notprovided with the phase adjusting film 41B can be used as thesemi-light-shielding portion having a small width between the phaseshifter and the opening. The single layered structure of thetransmittance adjusting film 41A generates a small phase differencebetween this structure and the opening. Thus, also when asemi-light-shielding portion having a small width is present between thephase shifter and the opening, a photomask having an effect of theoutline enhancement method can be formed while suppressing peeling ofthe film constituting the semi-light-shielding portion having a smallwidth. For example, in this embodiment, the half-tone film 41 made ofthe single layered thin light-shielding film is used for the entiresemi-light-shielding portion formation region. However, instead of this,the single layered structure of half-tone film 41 is used as thesemi-light-shielding portion between the phase shifter and the opening,and the multilayered structure of the half-tone film 41 and the phaseadjusting film formed thereon can be used as the semi-light-shieldingportion for the other regions.

In the first to fourth embodiments, it is assumed that all the portionsexcept the opening (light-transmitting portion) and the phase shifter(peripheral portion) in the photomask are semi-light-shielding portions.However, the portion in the photomask that is apart from each of theopening and the phase shifter by a sufficient distance, that is, adistance (=2×λ/NA (λ is the wavelength of exposure light, and NA is thenumerical aperture of a reduction projection optical system of anexposure apparatus)) that allows an influence of optical interferenceeffects from each of the opening and the phase shifter to be ignored maybe a complete light-shielding portion.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1-28. (canceled)
 29. A method for forming a pattern that uses aphotomask, comprising the steps of: a) forming a resist film on asubstrate; b) irradiating the resist film with the exposure light viathe photomask; and c) developing the resist film irradiated with theexposure light so as to pattern the resist film, wherein the photomaskcomprises on a transparent substrate: a semi-light-shielding portionhaving a light-shielding property with respect to the exposure light; alight-transmitting portion surrounded by the semi-light-shieldingportion and having a light-transmitting property with respect to theexposure light; and a peripheral portion surrounded by thesemi-light-shielding portion and positioned in a periphery of thelight-transmitting portion, the semi-light-shielding portion and thelight-transmitting portion transmit the exposure light in a same phase,the peripheral portion transmits the exposure light in a phase oppositeto that of the semi-light-shielding portion and the light-transmittingportion, and is spaced apart from the light-transmitting portion by apredetermined distance, a surface of the transparent substrate in aformation region for the light-transmitting portion is exposed, a firstphase shift film that transmits the exposure light in a phase oppositeto that of the light-transmitting portion is formed on the transparentsubstrate in a formation region for the peripheral portion, the firstphase shift film and a second phase shift film that transmits theexposure light in a phase opposite to that of the light-transmittingportion are laminated sequentially on the transparent substrate in aformation region for the semi-light-shielding portion, and amultilayered structure of the first phase shift film and the secondphase shift film has a transmittance that allows the exposure light tobe transmitted partially and transmits the exposure light in a samephase as that of the light-transmitting portion.
 30. The method forforming the pattern according to claim 29, wherein the first phase shiftfilm of the photomask has a first transmittance adjusting film and afirst phase adjusting film formed on the first transmittance adjustingfilm, the first transmittance adjusting film of the photomask transmitsthe exposure light in a same phase as that of the light-transmittingportion and has a relatively low transmittance with respect to theexposure light, and the first phase adjusting film transmits theexposure light in a phase opposite to that of the light-transmittingportion and has a relatively high transmittance with respect to theexposure light.
 31. The method for forming the pattern according toclaim 29, wherein the second phase shift film of the photomask has asecond transmittance adjusting film and a second phase adjusting filmformed on the second transmittance adjusting film, the secondtransmittance adjusting film of the photomask transmits the exposurelight in a same phase as that of the light-transmitting portion and hasa relatively low transmittance with respect to the exposure light, andthe second phase adjusting film of the photomask transmits the exposurelight in a phase opposite to that of the light-transmitting portion andhas a relatively high transmittance with respect to the exposure light.32. The method for forming the pattern according to claim 29, whereinthe first phase shift film of the photomask has a first phase adjustingfilm that transmits the exposure light in a phase opposite to that ofthe light-transmitting portion, the second phase shift film of thephotomask has a second phase adjusting film that is formed on the firstphase adjusting film and transmits the exposure light in a phaseopposite to that of the light-transmitting portion, and a transmittanceadjusting film having a lower transmittance than that of the phaseadjusting films with respect to the exposure light is formed between thefirst phase adjusting film and the second phase adjusting film.
 33. Themethod for forming the pattern according to claim 29, wherein theperipheral portion of the photomask is composed of a ring-shaped regionwhich is positioned in a periphery of the light-transmitting portion,and a part of the semi-light-shielding portion, which is ring-shaped, isinterposed between the peripheral portion and the light-transmittingportion.
 34. The method for forming the pattern according to claim 29,wherein the light-transmitting portion of the photomask has a polygonalshape, the peripheral portion of the photomask is composed of aplurality of rectangular regions, each region being positioned so as toface each side of the light-transmitting portion, and a part of thesemi-light-shielding portion is interposed between the peripheralportion and the light-transmitting portion.
 35. The method for forming apattern according to claim 29, wherein in the step of b), off-axisillumination is used to irradiate with the exposure light.
 36. A methodfor forming a pattern that uses a photomask, comprising the steps of: a)forming a resist film on a substrate; b) irradiating the resist filmwith the exposure light via the photomask; and c) developing the resistfilm irradiated with the exposure light so as to pattern the resistfilm, wherein the photomask comprises on a transparent substrate: asemi-light-shielding portion having a light-shielding property withrespect to the exposure light; a light-transmitting portion surroundedby the semi-light-shielding portion and having a light-transmittingproperty with respect to the exposure light; and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion, the semi-light-shieldingportion and the light-transmitting portion transmit the exposure lightin a same phase, the peripheral portion transmits the exposure light ina phase opposite to that of the semi-light-shielding portion and thelight-transmitting portion, and is spaced apart from thelight-transmitting portion by a predetermined distance, a surface of thetransparent substrate in a formation region for the light-transmittingportion is exposed, a semi-light-shielding film that has a transmittanceallowing the exposure light to be transmitted partially and transmitsthe exposure light in a same phase as that of the light-transmittingportion is formed on the transparent substrate in thesemi-light-shielding portion formation region, and thesemi-light-shielding film with a reduced thickness is formed on thetransparent substrate in a formation region for the peripheral portion,the thickness being such an extent that the exposure light istransmitted in a phase opposite to that of the light-transmittingportion.
 37. The method for forming a pattern according to claim 36,wherein the semi-light-shielding film of the photomask has atransmittance adjusting film formed on the transparent substrate and aphase adjusting film formed on the transmittance adjusting film, thetransmittance adjusting film of the photomask transmits the exposurelight in a same phase as that of the light-transmitting portion and hasa relatively low transmittance with respect to the exposure light, andthe phase adjusting film of the photomask has a relatively hightransmittance with respect to the exposure light, the phase adjustingfilm of the photomask in a formation region for the semi-light-shieldingportion has a thickness that transmits the exposure light in a samephase as that of the light-transmitting portion, and the phase adjustingfilm of the photomask in a formation region for the peripheral portionhas a thickness that transmits the exposure light in a phase opposite tothat of the light-transmitting portion.
 38. The method for forming apattern according to claim 36, wherein the semi-light-shielding film ofthe photomask has a phase adjusting film formed on the transparentsubstrate and a transmittance adjusting film formed only on the phaseadjusting film in the semi-light-shielding portion formation region, thetransmittance adjusting film of the photomask transmits the exposurelight in a same phase as that of the light-transmitting portion and hasa relatively low transmittance with respect to the exposure light, andthe phase adjusting film of the photomask has a relatively hightransmittance with respect to the exposure light, the phase adjustingfilm of the photomask in a formation region for the semi-light-shieldingportion has a thickness that transmits the exposure light in a samephase as that of the light-transmitting portion, and the phase adjustingfilm of the photomask in a formation region for the peripheral portionhas a thickness that transmits the exposure light in a phase opposite tothat of the light-transmitting portion.
 39. The method for forming apattern according to claim 36, wherein the peripheral portion of thephotomask is composed of a ring-shaped region which is positioned in aperiphery of the light-transmitting portion, and a part of thesemi-light-shielding portion of the photomask, which is ring-shaped, isinterposed between the peripheral portion and the light-transmittingportion.
 40. The method for forming a pattern according to claim 36,wherein the light-transmitting portion of the photomask has a polygonalshape, the peripheral portion of the photomask is composed of aplurality of rectangular regions, each region being positioned so as toface each side of the light-transmitting portion, and a part of thesemi-light-shielding portion is interposed between the peripheralportion and the light-transmitting portion.
 41. The method for forming apattern according to claim 36, wherein in the step of b), off-axisillumination is used to irradiate with the exposure light.
 42. A methodfor forming a pattern that uses a photomask, comprising the steps of: a)forming a resist film on a substrate; b) irradiating the resist filmwith the exposure light via the photomask; and c) developing the resistfilm irradiated with the exposure light so as to pattern the resistfilm, wherein the photomask comprises on a transparent substrate: asemi-light-shielding portion having a light-shielding property withrespect to the exposure light; a light-transmitting portion surroundedby the semi-light-shielding portion and having a light-transmittingproperty with respect to the exposure light; and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion, the semi-light-shieldingportion and the light-transmitting portion transmit the exposure lightin a same phase, the peripheral portion transmits the exposure light ina phase opposite to that of the semi-light-shielding portion and thelight-transmitting portion, a surface of the transparent substrate in aformation region for the light-transmitting portion is exposed, asemi-light-shielding film that has a transmittance that allows theexposure light to be transmitted partially and transmits the exposurelight in a same phase as that of the light-transmitting portion isformed on the transparent substrate in the semi-light-shielding portion,and the transparent substrate in a formation region for the peripheralportion is dug down such that a thickness thereof is such an extent thatthe exposure light is transmitted in a phase opposite to that of thelight-transmitting portion.
 43. The method for forming a patternaccording to claim 42, wherein the semi-light-shielding film of thephotomask has a transmittance adjusting film formed on the transparentsubstrate and a phase adjusting film formed on the transmittanceadjusting film, the transmittance adjusting film of the photomask has arelatively low transmittance with respect to the exposure light, and thephase adjusting film of the photomask has a relatively hightransmittance with respect to the exposure light.
 44. The method forforming a pattern according to claim 42, wherein the peripheral portionof the photomask is in contact with the light-transmitting portion. 45.The method for forming a pattern according to claim 44, wherein theperipheral portion of the photomask is composed of a ring-shaped regionwhich is in contact with a periphery of the light-transmitting portion.46. The method for forming a pattern according to claim 44, wherein thelight-transmitting portion of the photomask has a polygonal shape, andthe peripheral portion of the photomask is composed of a plurality ofrectangular regions, each region being in contact with each side of thelight-transmitting portion.
 47. The photomask according to claim 42,wherein the peripheral portion of the photomask is spaced apart from thelight-transmitting portion by a predetermined distance.
 48. The methodfor forming a pattern according to claim 47, wherein the peripheralportion of the photomask is composed of a ring-shaped region which ispositioned in a periphery of the light-transmitting portion, and a partof the semi-light-shielding portion, which is ring-shaped, is interposedbetween the peripheral portion and the light-transmitting portion. 49.The method for forming a pattern according to claim 47, wherein thelight-transmitting portion of the photomask has a polygonal shape, theperipheral portion of the photomask is composed of a plurality ofrectangular regions, each region being positioned so as to face eachside of the light-transmitting portion, and a part of thesemi-light-shielding portion is interposed between the peripheralportion and the light-transmitting portion.
 50. The method for forming apattern according to claim 42, wherein in the step of b), off-axisillumination is used to irradiate with the exposure light.
 51. A methodfor forming a pattern that uses a photomask, comprising the steps of: a)forming a resist film on a substrate; b) irradiating the resist filmwith the exposure light via the photomask; and c) developing the resistfilm irradiated with the exposure light so as to pattern the resistfilm, wherein the photomask comprises on a transparent substrate: asemi-light-shielding portion having a light-shielding property withrespect to the exposure light; a light-transmitting portion surroundedby the semi-light-shielding portion and having a light-transmittingproperty with respect to the exposure light; and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion, the light-transmittingportion has a polygonal shape, the peripheral portion is composed of aplurality of rectangular regions, each region being positioned so as toface each side of the light-transmitting portion, thesemi-light-shielding portion and the light-transmitting portion transmitthe exposure light in a same phase, the peripheral portion transmits theexposure light in a phase opposite to that of the semi-light-shieldingportion and the light-transmitting portion, a surface of the transparentsubstrate in a formation region for the light-transmitting portion isexposed, a first phase shift film that transmits the exposure light in aphase opposite to that of the light-transmitting portion is formed onthe transparent substrate in a formation region for the peripheralportion, the first phase shift film and a second phase shift film thattransmits the exposure light in a phase opposite to that of thelight-transmitting portion are laminated sequentially on the transparentsubstrate in a formation region for the semi-light-shielding portion,and a multilayered structure of the first phase shift film and thesecond phase shift film has a transmittance that allows the exposurelight to be transmitted partially and transmits the exposure light in asame phase as that of the light-transmitting portion.
 52. The method forforming a pattern according to claim 51, wherein the first phase shiftfilm of the photomask has a first transmittance adjusting film and afirst phase adjusting film formed on the first transmittance adjustingfilm, the first transmittance adjusting film of the photomask transmitsthe exposure light in a same phase as that of the light-transmittingportion and has a relatively low transmittance with respect to theexposure light, and the first phase adjusting film of the photomasktransmits the exposure light in a phase opposite to that of thelight-transmitting portion and has a relatively high transmittance withrespect to the exposure light.
 53. The method for forming the patternphotomask according to claim 51, wherein the second phase shift film ofthe photomask has a second transmittance adjusting film and a secondphase adjusting film formed on the second transmittance adjusting film,the second transmittance adjusting film of the photomask transmits theexposure light in a same phase as that of the light-transmitting portionand has a relatively low transmittance with respect to the exposurelight, and the second phase adjusting film of the photomask transmitsthe exposure light in a phase opposite to that of the light-transmittingportion and has a relatively high transmittance with respect to theexposure light.
 54. The method for forming the pattern photomaskaccording to claim 51, wherein the peripheral portion of the photomaskis in contact with the light-transmitting portion.
 55. The method forforming a pattern according to claim 51, wherein in the step of b),off-axis illumination is used to irradiate with the exposure light. 56.The method for forming a pattern according to claim 29, wherein in thephotomask, a transmittance of the semi-light-shielding portion withrespect to the exposure light is 6% or more and 15% or less.
 57. Themethod for forming a pattern according to claim 36, wherein in thephotomask, a transmittance of the semi-light-shielding portion withrespect to the exposure light is 6% or more and 15% or less.
 58. Themethod for forming a pattern according to claim 42, wherein in thephotomask, a transmittance of the semi-light-shielding portion withrespect to the exposure light is 6% or more and 15% or less.
 59. Themethod for forming a pattern according to claim 51, wherein in thephotomask, a transmittance of the semi-light-shielding portion withrespect to the exposure light is 6% or more and 15% or less.